China has the largest area of tree plantations in the world, and how to maintain the long-term stability of plantations has become one of the major challenges in the context of climate change. Pinus sylvestris var. mongolica is one of the most important coniferous evergreen tree species in the well-known “Three-North” Shelterbelt Construction Program in China, due to its properties of tolerance to drought, low temperature, and open land condition. Afforestation with P. sylvestris var. mongolica in northern China provides great benefits to environmental protection and ecosystem carbon fixation. However, with the growth of the stands and the ongoing climate change, P. sylvestris var. mongolica plantations in a fragile habitat of sandy land have been subjected to increasingly severe water stresses. Typically, the phenomenon of premature dieback has occurred in some of the P. sylvestris var. mongolica plantations, such as at the sites of Zhanggutai in the southern edge of Horqin Sandy Land, which causes great concerns on the stability of the local ecosystems. Based on recollections of studies on the basic biological characteristics and introduction history of P. sylvestris var. mongolica, we summarized the recent research achievements in understanding the forest-water relationships in P. sylvestris var. mongolica plantations, and examined the main contradictions in the forest-water relationships in P. sylvestris var. mongolica plantations under the climate change scenario. We recommend adjustment of several stand management measures based on the compromised forest-water relationships: (1) turning the single goal for environmental protection into multi-objectives with balanced consideration for stand structural stability, carbon sequestration, and sustainable development; (2) adopting more measures for improving soil conditions rather than for developing forest landscapes; and (3) establishing the sustainable shelterbelts by combining afforestation with natural regeneration rather than by merely depending on natural regeneration processes. Based on the condition of fragile sandy land and climate change, we should still regard P. sylvestris var. mongolica as a pioneer and construction tree species. In consideration of the principle of “determining forest cover by water supply”, the uneven-aged forest stands can be established by conducting alternate-row harvesting followed by replanting. As a result, the environmental protection function and carbon sequestration capacity can be continuously improved, the ecological services and productivity can be maximized, and the biodiversity and stability of the ecosystem can be protected and guaranteed. The findings from this study can be of important values for guiding the systematic management of northern ecological shelterbelts.

Sexual selection and sexual conflict are important driving forces for the diversity of reproductive traits and the evolution of sexual system in plants. These two interrelated but different theories could benefit our understanding of plant reproductive ecology. Although the sexual selection and sexual conflict have been considered in plant reproduction ecology, rarely related domestic research involved and applied them. Hence, we review the primary theories and research progress of sexual selection and sexual conflict profoundly in this paper. First, we review the development status and application basis of sexual selection and sexual conflict in plant researches. Second, we introduce the effects and mechanisms of sexual selection and sexual conflict during the process of plant reproduction, including pre-pollination and post-pollination stages, and emphasize the important influences of environmental factors. Finally, we summarize the shortcomings in previous research and point out the possible research directions in the future. In a word, we hope that this review could attract more attention to the importance of sexual selection and sexual conflict, and promote its application and development in plant reproductive biology.

Aims Climate change is significantly altering the phenology and growth pattern of alpine plants related to their resource allocation strategies, thereby changing the functioning of alpine ecosystems. The aim of this study is to explore responses of reproductive phenology and vegetative growth of alpine plants to climate warming on the Qingzang Plateau.

Methods Experimental warming was achieved using infrared heating. From 2017 to 2018, we measured the reproductive phenology (leaf out, flower bud, flower and fruit time) and maximum height of 15 common alpine plants (account more than 80% of the total above biomass) under non-competitive condition via common garden experiment.

Important findings Our results showed that: (1) Experimental warming significantly advanced the leaf out, flower bud and first flowering day of legumes by (8.21 ± 1.81), (9.14 ± 2.41) and (10.14 ± 2.05) d, respectively. In addition, warming significantly prolonged the flowering duration of legumes by (6.14 ± 1.52) d. This result implied that different functional groups showed different responses under warming. The reproductive phenology of most alpine plants advanced, and the flowering duration was prolonged under warming, suggesting that more resources was allocated to reproductive growth. (2) In addition, experimental warming significantly reduced the height of forbs by (3.58 ± 0.96) cm, but not of other functional groups. Different species have differential responses to warming in different year. In summary, the alpine plant community on the Qingzang Plateau may start the reproductive stage earlier, hence reducing the resource allocation for vegetative growth under future warming conditions. In addition, due to different responses of the reproductive capacity and vegetative growth of various species to temperature change, climate warming may change the coverage of various species, and then alter the composition of species in the community, and then change the function of alpine ecosystem.

Aims Subalpine dark coniferous forests are an important representative of the cold-temperate coniferous forests in China. Dark coniferous forests dominated by spruce (Piceaspp.) and fir (Abies spp.) are the main body of subalpine forests on the eastern edge of the Qingzang Plateau and an important ecological defense in the upper reaches of the Yangtze River in China. In this study, we examined the community composition and structure of such a dark coniferous forest based on the first census data of the 25.2 hm² Wanglang forest dynamics plot in western Sichuan.

Methods The plot was established following the standard protocol of Forest Global Earth Observation Network (ForestGEO) and all free-standing stems with diameter at breast height (DBH) ≥ 1 cm were tagged, mapped, measured and identified to species.

Important findings A total of 56 574 individuals belonging to 46 species, 27 genera and 15 families are tagged, including 4 coniferous species, 6 evergreen broad-leaved species and 36 deciduous broad-leaved species. There are 13 rare species (≤1 individuals per hm²), accounting for 28.26% of the total number of species and 0.16% of the total number of individuals in the plot. Abies fargesiivar. faxoniana(9 440 individuals) and P. purpurea (1 645 individuals) are the dominant and constructive species in canopy, accounting for 26.03% and 10.69% of the total importance value, and 55.22% and 24.84% of the total basal area (37.87 m²·hm^-2), respectively. The number of individuals of deciduous broad-leaved species accounted for 78.48% of the total individuals. Among them, Philadelphus purpurascens, Lonicera nervosaand Euonymus frigidusare the dominant species in shrub layer. The number of individuals of evergreen broad-leaved species is 268, and all these species belong to genus Rhododendron. The composition of the size distribution shows typical characteristics of old-growth forests. Picea purpurea is the largest tree species (max DBH = 127.07 cm) and the mean basal area (0.14 ± 0.18) m² is much higher than that of A. fargesiivar. faxoniana(0.056 ± 0.11) m². The size class distribution of all woody species shows an inverse J-shaped distribution, indicating that the community is in a stable and healthy recruitment state. Results of the point pattern analysis reveal that the five dominant tree species (important values ≥5) all show aggregated distribution patterns. However, as the spatial scale increases, all five species tend to be randomly distributed. The results of this study provide basic information for future studies on the diversity maintenance and regeneration mechanisms of subalpine dark coniferous forests in western Sichuan, and the conservation and management of this unique forest ecosystem.

Aims Seed size and number variation is the core issue in the study of plant fitness. Exploring the grazing effects of different large herbivore assemblage on the relationship between seed size and number of dominant species in Kobresia grasslands, is helpful to understand the reproductive strategy and population regeneration mechanism.

Methods This research was conducted on the technical platform of adaptive management of alpine grassland- livestock system on the Qingzang Plateau. There were six grazing treatments: no grazing (control), single yak grazing, single Xizang sheep grazing, yak:Xizang sheep grazing ratios of 1:2, 1:4 and 1:6. And we analyzed the reproductive characteristics of K. humilis, the relationship between seed size, seed number and its tradeoff.

Important findings The results showed that: 1) Grazing treatment increased the seed size and seed number of K. humilis by more than 15% and 30%, respectively. The variation coefficient of seed size decreased by at least 15% under other grazing treatments except for yak:Xizang grazing ratio of 1:2. While the variation coefficient of seed number decreased by more than 25%. 2) Pearson correlation analysis showed that there were positive correlation between seed size, seed number and reproductive traits under grazing treatments. 3) Grazing treatments increased the tradeoff between seed size and seed number which was largely affected by the mass of single reproductive branch. The results suggest that even at moderate grazing, livestocks are still the limiting factors for the acquisition of resources. Long-term grazing changes the potential relationship and tradeoff among the traits of K. humilis, stabilizes the features of seed size and seed number. The reproductive strategy of K. humilis is optimized by increasing seed size and seed number, which improves the near-ground competitiveness and fitness of offsprings.

Aims Exploring the spatial distribution patterns and interactions of populations can help elucidate the underlying driving factors in population structure construction and the maintenance mechanism of spatial distribution. It guides the allocation, and management of different populations in the forest ecosystems, and also provides a scientific basis for local ecological environment protection and regional resource development.

Methods In this study, Picea crassifolia was selected as the research object. Three repeated plots with an area of 1 hm² were set up in the Pailugou Watershed of the Qilian Mountains, and all individual trees with a diameter at breast height (DBH) ≥1 cm were measured and recorded. The spatial patterns and intraspecific interactions of Picea crassifolia were analyzed by using a pair-correlation function (univariate and bivariate pair-correlation function) and mark correlation function (marked correlation function, marked variogram function, and Schlather’s I(r) function).

Important findings (1) The diameter class distribution of P. crassifolia population was continuous, with an inverted “J” type structure. (2) Picea crassifolia as a whole, saplings, and young trees showed a small-scale aggregation distribution, and gradually tended to random distribution with the increase of spatial scale. Medium trees showed a random distribution pattern on the whole observation scale, while large trees showed a regular distribution on the small scale and random distribution on the large scale. (3) Large trees of P. crassifolia showed small-scale negative correlations with other size class individuals and middle-scale positive correlations. There were strong positive correlations between medium and young trees, and between sapling and young trees at a small to medium scale, and they gradually changed to no correlation with the increase of spatial scale. (4) Individual characteristics of P. crassifolia showed high correlations, strong inhibitions, and significant symmetry competitions on a small to medium scale.

Aims In view of the overarching significance for tree function and survival, it is essential to explore the environmental influences on tree development. Our objective was to clarify the altitudinal differences in the onset and offset of each stage of tree radial growth, to analyze the response of cambium activity and xylem differentiation to temperature at different altitudes, and to identify low temperature threshold for radial growth of trees.

Methods Weekly microcores and hourly in situ climate data were collected at 3 600, 3 800 and 4 000 m along the altitude gradient of Abies georgei var. smithii forest in Jiaozi Mountain, Yunnan.

Important findings The results showed that: (1) There were differences in the phenology of radial growth at three altitudes. The onset of radial growth was delayed by 4.7 d per 100 m, the end of radial growth was advanced by 7.2 d per 100 m, and the growing season was shortened by 12.8 d per 100 m with increasing altitude; (2) The radial growth of Abies georgei var. smithii at different altitudes had similar low temperature thresholds (about 5 °C), and temperature controlled the onset of cambium activity and the end of xylem differentiation; (3) The degree of cell division activity at different altitude decreased at higher temperatures (around the summer solstice), and photoperiod was involved in the regulation of the end of cambium activity to ensure the completion of cell mature before the freezing. The relationship between the cambium activity and altitude-induced temperature change is weak. The photoperiod may be involved in regulating the end of cambium activity to ensure the completion of cell mature before the freezing. This study contributes to understand the response mechanisms of tree growth dynamics to climate change and provides a scientific basis for better adaptation and response to climate change.

Aims Flower syndrome and pollination characteristics are the basis and main driving forces of the evolutionary success of flowering plants. Lycium ruthenicum is a national second-class protected plant distributed in northwest China, with two flower morphs, i.e. homostylous flower (style length is similar to stamen length) and flower with approach herkogamy (style length is longer than stamen length). However, little is known about the flower syndrome and pollination characteristics of the different flower types of L. ruthenicum.

Methods In this study, we compared the flowering phenology, flower characteristics, flower reward, and pollination characteristics of two different flower morphs of L. ruthenicum.

Important findings In Kashi natural populations, there is no significant difference in the height of sexual organs of homostylous flower, but it is significant in the herkogamous flowers. The corolla diameter, corolla tube length, number of ovules of homostylous flowers are higher than that of herkogamous flowers. The stamen-stigma distance, number of pollen and pollen/ovule (P/O) of herkogamous flowers are higher than that of homostylous flower. The proportion of homostylous individuals (68%) is higher than that of herkogamous (32%). Population and individual level flowering times were significantly different between the flower morphs and were longer for homostylous flower individuals ((117.00 ± 2.25) d, (101.65 ± 1.98) d) than that of herkogamous flower individuals ((26.00 ± 1.00) d, (18.75 ± 1.00) d), but the longevity of herkogamy flowers ((4.50 ± 0.14) d) are longer than that of homostylous flowers ((3.13 ± 0.11) d). At early flower stage (purple phase) the nectar volume of two morphs is significantly higher than late stage (white phase). In the purple phase the main pollinators were Bombussp., Apis mellifera and Syrphidae, and the visiting frequency and duration of stay on the homostylous flowers are higher than that of herkogamy flowers. In the white phase, the main pollinators on the herkogamous flower have higher visiting frequency than that of homostylous flower. At the different phases the number of pollen deposited on the stigma, pollen removal rate, pollination efficiency of homostylous flowers are higher than that of herkogamous flowers. The fruit and seed set of homostylous flowers are higher than that of herkogamous flowers. Under the extreme environment of sandstorms in southern Xinjiang, homostylous flowers can secure reproduction through high self-compatibility, and herkogamous flowers will increase outcrossing rate in the population. These differences in flower traits and pollination adaptations may be the main factor affecting the reproductive success of L. ruthenicum.

Aims The plant mortality induced by drought has significant impact on forest ecosystems around the world. It thus has brought intensive research attention on the plant adaptive strategy to drought in the field of physiological ecology. This study aims to investigate the differences in adaptation strategies to drought between two dominant species in arid desert areas, i.e., Haloxylon ammodendron and Alhagi sparsifolia.

Methods Three types of functional traits (i.e., leaf, photosynthetic and hydraulic traits) of A. sparsifolia and H. ammodendron were measured in response to a natural drought gradient (mild, moderate and severe) in Ebinur Lake Nature Reserve in Xinjiang, China. The changes of functional traits with drought gradient, and the differences of functional traits and adaptation strategies to drought between the two species were analyzed.

Important findings The functional traits of A. sparsifolia and H. ammodendron changed differently across drought gradient. All the functional traits were significantly different between the two species except for leaf dry matter content. However, the differences in functional traits between the two species showed a decrease due to the synergetic influence of drought stress and species convergence. Pearson correlation among the traits for the two species indicated that only 10 pairs of functional traits are significantly correlated for A. sparsifolia, while 15 pairs were significantly correlated for H. ammodendron. Principal component analysis (PCA) showed that two typical trait combinations related to drought resistance can be obtained from 11 functional traits of H. ammodendron, namely drought resistance-carbon acquisition group and drought resistance group. However, the trait combinations in coping with drought were not identified for A. sparsifolia. The results suggested that A. sparsifolia,was a conservative species, having greater drought tolerance than H. ammodendron. The traits in A. sparsifolia was less associated than that in H. ammodendron. In contrast, H. ammodendron used the trade-offs and compensatory relationships among functional traits to reduce drought stress. This study provided insights into the relationship between functional traits and drought adaptation strategies of different plant life forms, which advanced the fundamental theories of plant physiological ecology, and provided implications and references for the protection and diversity maintenance of desert ecosystem.

Aims Arid and semi-arid areas account for about 30% of the total global land area. Plant growth in these areas is more susceptible to drought stress. Both atmospheric drought and soil drought can affect plant growth. Although there have been many experimental studies on the effects of atmospheric drought and soil drought on plant growth, the specific mechanism is not clear.

Methods In this study, the differential effects of air and soil humidification on the growth characteristics of young Pinus sylvestris var. mongolicatrees were investigated by manipulation experiments of altering air humidity and soil water content.

Important findings The results showed that: 1) Compared with the control, air humidification significantly reduced vapor pressure deficit by 20.5%, and air humidification and soil humidification significantly increased soil moisture by 23.4% and 21.3%, respectively; 2) Air humidification significantly increased leaf density, soil humidification significantly increased twig diameter, and air and soil humidification significantly promoted the growth of leaves and twigs; 3) Taking into consideration of the effect of humidification treatment on radial growth and the analysis with structural equation model, the results showed that soil humidification directly promoted the stem radial growth, and the significant positive effects of air humidification on radial growth is due to the direct effect of the decrease in vapor pressure deficit, and the indirect effect in the increase of soil moisture caused by air humidification. This study revealed distinct responses of young P. sylvestris var. mongolica tree growth to atmospheric water and soil water changes.

Aims The tree decline and death caused by drought stress under global climate change is a topic of general interest in ecological research. Different tree species in the same habitat can adopt various hydraulic strategies to maintain water balance in order to deal with drought stress. Populus tomentosa and Acer truncatum are the main tree species in plantations in the North China Plain. Studies on their hydraulic structure and dynamics of non-structural carbohydrate (NSC) content during drought-rehydration can reveal their hydraulic regulation strategies and provide theoretical basis for scientific management of water balance in plantations in north China under the background of global climate change.

Methods By using the saplings of P. tomentosa and A. truncatum distributed in the same habitat, we measured the hydraulic structure parameters, such as the resistance to embolism and hydraulic safety margin of stem, hydraulic areas, osmotic potential at leaf turgor pressure loss point, etc. Dehydration and rehydration were carried out to investigate the dynamics of stem NSC content, and to examine the repair capacity of xylem embolism in the rehydration stage after drought stress removel.

Important findings The results showed that the water potential of P. tomentosa (-1.289 MPa) when xylem hydraulic conductivity lost 50% was higher than that of A. truncatum(-2.894 MPa). Populus tomentosa also presented lower osmotic potential at turgor pressure loss point, narrower hydraulic safety margin, smaller wood density, and tended to have anisohydry behavior of stomatal regulation, indicating that it was prone to embolism characterized with dehydration and drought tolerance at low water potential, and tended to have more risky water regulation strategies. Acer truncatum survived drought stress by “delayed dehydration” at high water potentials, and tended to have conservative water regulation strategy. In the dehydration-rehydration experiment, the contents of soluble sugar, starch and non-structural carbohydrate in stem of P. tomentosa decreased first and then increased, while those of A. truncatum increased first and then decreased, and P. tomentosa showed a higher embolic repair ability than A. truncatum, which was related to the difference of stem NSC content. The higher embolism repair ability of P. tomentosa can provide hydraulic safety guarantee for risky water regulation strategies and drought tolerance strategy. There were significant differences between P. tomentosa and A. truncatum in the regulation of hydraulics, which might be related to the characteristics of life history.

Aims Malus sieversii, being listed as a national second-class protected plant in China, is recognized as one of the wild ancestors for domesticated apple. It is fragmentally distributed in arid mountains of the Central Asian. Here, we aimed to investigate the main environment variables shaping population genetic variations and the genetic adaptation in response to these environment variables for this species.

Methods We collected ten M. sieversii populations from Yili Prefecture of China, Kazakhstan and Kyrgyzstan. Single nucleotide polymorphism (SNP) dataset was generated by SLAF-seq. Population genetic structure was inferred using the ADMIXTURE software and principal component analysis. Main environment variables shaping population genetic variations were assessed by gradient forest analysis and redundancy analysis. Tests of associated outlier loci with environmental variations were carried out by latent factor mixed models, which was used to access genetic signatures of local adaptation.

Important findings Ten populations were clustered into two lineages. Lineage A dominated eastern populations, while Lineage B mainly distributed in western populations. Two lineages were mixed in central populations, and an obvious pattern of geographical substitute along the longitude direction was found. The most important environment variables that influence the change of allele frequency for M. sieversii populations were temperature annual range (bio 07) and temperature seasonality (bio 04). Fifteen loci having a significant association with environmental variables were successfully annotated. Most of them were genes related to abiotic stress responses and stress-induced physiological adaptations, such as drought, salt and cold. In conclusion, temperature variation is the main factor that drives the adaptation of M. sieversii to environments. Physiological adaptations, as indicated by the above candidate loci, were most likely the main mechanism related to abiotic stress response.

Aims This study aimed to study the effects of two young mixed plantations of Parashorea chinensis (an endangered native tree species) on the functional characteristics and carbon source utilization of the soil microbial community, so as to select the suitable afforestation mode of P. chinensis and maintain sustainable management of forests by changing pure Eucalyptus plantation into mixed plantations with heterogeneous structure.

Methods The functional diversity of soil microbes and their utilization of six carbon sources in mixed and pure plantations of P. chinensis were compared and analyzed using the Biolog-ECO technique, and a correlation analysis was further carried out incorporating soil physicochemical properties.

Important findings (1) The Shannon-Wiener, Simpson and McIntosh diversity index of the microbe community in mixed plantations of P. chinensis and E. grandis × E. urophylla were the highest, and their soil microbial functional diversity was significantly higher than that of pure plantations. (2) The carbon source utilization and microbial quantity of soil microbes in the mixed plantations were higher than those in the pure plantation, and decreased with the deepening of the soil layer. The utilization of phenolic acid by soil microbes in mixed and pure plantations was the highest, followed by amines, with polymers at the lowest level, and the difference was that mixed and pure plantations were more dependent on amino acids and carboxylic acids, respectively. (3) The soil moisture conditions and the content of organic matter, total nitrogen, total potassium and available nutrients in the mixed forest of P. chinensis were higher. In addition, the vertical distribution of other nutrients except total phosphorus and total potassium showed obvious surface aggregation. (4) Environmental factors analysis showed that soil pH, organic matter and potassium were the main driving factors causing significant differences in soil microbial functional diversity and carbon source utilization between mixed and pure plantations, as well as different soil layers. In summary, the mixed afforestation model of P. chinensis has a significant impact on soil microbial community and their habitats. Especially, P. chinensis mixing with E. grandis × E. urophylla may effectively improve the metabolic activity and functional diversity of soil microbes, and promote the decomposition of organic matter. Compared with the pure forest, the mixed forest improved soil quality and fertility to some extent, and created a better soil environment and light conditions for the growth of young P. chinensis saplings.