Aims Litterfall is a measure of the metabolic product of forest plants during their growth. It plays an important part in the fluxes and recycling of matter and energy. The metabolic theory of ecology posits that there exist allometric relationships among different organs of a plant. However, all these scaling relationships do not take into account the potential contribution of litterfall, and hence much remains unknown about the allometric relationships among the different components of litterfall. In this study, we analyze the allometric relationships between component as well as the allometric relationships of the total litterfall with different components.
Methods We compiled data on forest litterfall from the literature published in Chinese journals and divided these data into evergreen forests and deciduous forests for analysis of the allometric relationships between components as well as the allometric relationships of the total litterfall with different components.
Important findings We found that the average amount of litterfall was 3810.34 kg·hm^-2·a^-1, 1019.07 kg·hm^-2·a^-1, and 767.95 kg·hm^-2·a^-1 as leaves, branches, and propagules, respectively. Compared with precipitation and stand age, temperature had a greater effect on forest litterfall production. An isometrical relationship was observed between leaves and the total litterfall, as L_L ∝ L_T ^0.96(L_L, leaf litterfall; L_T, total litterfall); whereas an allometric relationship was found between the propagules and the total litterfall as L_P ∝ L_T^1.84(L_P, propagule litterfall), and between the branches and the total litterfall as L_B ∝ L_T^1.61 (L_B, branch litterfall), respectively. Significant allometric relationships were also observed among different components, with exponents all less than 1.0 in each case. Allometric relationships of the total litterfall with different components were approximately the same between the evergreen forests and the deciduous forests. The allometric relationships found in this study provide valuable insights into the investigation and estimation of forest productivity.

Aims Soil fauna has an important effect on litter nutrient release in cold regions, and the effect could vary with litter types and be controlled by environmental factors such as temperature and precipitation. Our objective was to characterize the effect of soil fauna on N and P dynamics during litter decomposition in subalpine and alpine forests.
Methods A field litterbag experiment was conducted in subalpine and alpine forests of western Sichuan, China, from November 2011 through October 2012. Samples of air-dried leaf litter for Salix paraplesia, Sabina saltuaria, Betula albosinensis, and Abies fargesii var. faxoniana were placed in nylon litterbags (20 cm × 20 cm, 10 g per bag) of two different mesh sizes (i.e. 3.00 mm and 0.04 mm). The amount of N and P released were investigated at different stages during the first year of decomposition, i.e., onset of freezing period, deep freezing period, thawing stage, early growing season, mid-growing season, and late growing season.
Important findings The N dynamics during decomposition differed between the leaf litter of broadleaf trees and that of coniferous trees: they were of a release-enrichment-release pattern in Salix paraplesia and B. albosinensis, and of a release-enrichment pattern in Sabina saltuaria and A. fargesii var. faxoniana. The P generally displayed a declining trend, but with an obvious enrichment process in the mid-growing season. During the first year of litter decomposition, soil fauna imposed a positive effect on N release, and a negative effect on P release. There was a significant difference in the amount of litter N and P released through soil fauna among different stages during the first year of decomposition. The amount of N released through soil fauna was positively related to the positive accumulated temperature; whereas the amount of P released through soil fauna was highly negatively related to the positive accumulated temperature. Soil fauna affected more on the litter of broadleaf trees than on the litter of coniferous trees in N and P dynamics during decomposition.

Aims Little study has been conducted to quantify plant water sources for Myricaria squamosa, which is a dominant alpine riparian shrub in the Qinghai Lake basin and plays a key role in maintaining riverine wetland system. The objective of this study was to quantify water sources for M. squamosa growing under different hydrological conditions.
Methods We collected the water samples from the xylem of M. squamosa, groundwater, river, and soils in the Qinghai Lake basin from June through September, and analyzed the seasonal variation of hydrogen stable isotope ratio (δD) in the xylem and potential water sources using stable hydrogen isotope tracer method. We then compared the differences in water sources for M. squamosa growing under two contrasting hydrological conditions.
Important findings Myricaria squamosa plants growing on the river bank mainly used groundwater and water from the river stream in June and July, with groundwater contributing up to 89% of water use in June and 55% in July and river stream contributing up to 86% in June and 65% in July, respectively; whilst in August, they used water mainly from the 0-20 cm soil layer; the water source in September was identifiable. In contrast, Myricaria squamosa plants growing approximately about 100 m away from the river bank mainly accessed the groundwater and river water in June (91% and 70%, respectively), and used water from the 0-60 cm soil layer during the rainy months July, August and September. Results suggest that M. squamosa plants on the river bank use mainly groundwater and river water; soil water was more important for those far away from the river bank. These are resulted from the responses of this shrub species to specific water conditions when growing under contrasting water regimes.

Aims Our general objective was to understand the effects of short-term phloem girdling on physiological performance in Karelinia caspia and Alhagi sparsifolia, concerning not only the impacts of degrees of girdling but also the differences in damage between the two plants under girdling treatment. Specifically, we want to know the mechanisms of the decline in photosynthesis under girdling treatment.
Methods We imposed three different types of girdling treatments, normal branch, semi-girdling, and full-girdling, and studied the reaction of photosynthetic pigments, chlorophyll fluorescence parameters in K. caspia and A. sparsifolia under the conditions of girdling after about 10 days.
Important findings The effects varied with the type of girdling treatments and differed between K. caspia and A. sparsifolia. There was no apparent effect on physiological parameters in K. caspia with semi-girdling treatment; whereas full-girdling significantly reduced chlorophyll content and carotenoids content in both K. caspia and A. sparsifolia. The full-girdling also constrained the primary photosynthetic reaction in K. caspica and A. sparsifolia, and damaged the structure and function of photosystem II (PSII), leading to reduction in the activity of PSII. The processes of absorption, transmission, conversion, and electron capture of light energy in photosynthetic organs were also constrained, and the energy used for dissipate significantly increased. We believe the degree of damage in K. caspia under full-girdling is more severe than in A. sparsifolia. As the disturbance in Cele Oasis is further exacerbated, whether the population of A. sparsifolia could adapt to this change better than K. caspia is still inclusive, because the resilience of plants is also an essential factor. There exist a carbohydrate-dependent mechanism in the effects on photosynthetic rate in K. caspia and A. sparsifolia subjected to girdling.

Aims Picea schrenkiana ssp. tianschanica is a major tree species in forest ecosystems in the Xinjiang Uygur Autonomous Region, West China, and plays an important role in the regional water conservation. 3,4-dihydroxy acetophenone (DHAP) is a principal autotoxic substance occurring in foliage and litter of P. schrenkiana ssp. tianschanica that causes suppressed natural regeneration in P. schrenkiana ssp. tianschanica forests. The objectives of this study were to investigate changes in the content of endogenous plant hormones during seed germination in P. schrenkiana ssp. tianschanica as affected by DHAP, and to elucidate the underlying physiological mechanisms in the autotoxic effects.
Methods We investigated the inter-relationships among DHAP treatment, seed germination, and changes in the concentration of endogenous plant hormones by measuring the contents of zeatin (ZT), gibberellin (GA₃), indole-acetic acid (IAA), and abscisic acid (ABA) during germination process in P. schrenkiana ssp. tianschanica seeds with or without DHAP treatment. The concentrations of plant hormones in germinating seeds were measured with the method of ultra performance liquid chromatography (UPLC).
Important findings Results showed that the impact of DHAP on seed germination in P. schrenkiana ssp. tianschanica depended on treatment concentrations, in the order of 5.0 mmol·L^-1 > 0.1 mmol·L^-1 > 1.0 mmol·L^-1 > control; treatments with DHAP reduced the concentrations of ZT and GA₃, delayed the peak occurrence of GA₃, and increased the concentration of ABA with a delayed peak occurrence under treatments of 1.0 and 5.0 mmol·L^-1 DHAP. Treatment with 5.0 mmol·L^-1 DHAP for 3-6 days greatly increased the level of IAA. 1-6 days of treatments with DHAP reduced the ZT/(GA₃ + IAA) ratio, and increased the IAA/ZT ratio and ABA/ZT ratio; the ABA/(ZT + GA₃ + IAA) ratio increased at 0.1 mmol·L^-1 DHAP and decreased at 5.0 mmol·L^-1 DHAP. It is suggested that DHAP treatment causes changes in the content and balance of endogenous plant hormones, leading to inhibition or delaying in seed germination in P. schrenkiana ssp. tianschanica.

Aims Polycyclic aromatic hydrocarbons (PAHs) are a large class of ubiquitously occurring persistent organic pollutants (POP). Plants can take up PAHs through atmospheric sedimentation and sewage irrigation, resulting in serious hazards on the food safety and human’s health. Our objective was to investigate the effects of fluoranthene (FLU) and benzo-a-pyrene (B[a]P) on growth, physiological performance, and quality of rape (Brassica chinensis), and to understand their patterns of accumulations in stem and leaves.
Methods Rape seedlings were transplanted to grow in soils with different rates of FLU and B[a]P addition, i.e. 0, 0.5, 1.0, 5.0, and 10.0 mg·kg^-1, respectively. Growth indicators including leaf length, leaf width, plant height and aboveground biomass, and physiological properties including photosynthetic rate (P_n), chlorophyll content, and the content of vitamin C were measured to determine the effects of the two PAHs on rape. Accumulations of FLU and B[a]P were measured by the method of high performance liquid chromatography (HPLC). Pearson correlation analysis was performed to investigate the relationships between the accumulations of the PAHs and various growth indicators.
Important findings We found that the accumulated concentrations of FLU and B[a]P in rapes increased with the level of FLU and B[a]P in soils. The accumulations of FLU in stems and leaves differed significantly (p < 0.05) among treatments with different rates of FLU addition. As compared with the control (CK), the accumulations of B[a]P in rapes significantly increased in treatments with 5.0 and 10.0 mg·kg^-1 B[a]P addition, and the highest amount of accumulation at 10 mg·kg^-1 was below the national food security standard. Low concentrations of FLU and B[a]P had positive effects on leaf length, leaf width and the aboveground biomass; whereas high concentrations had negative impacts. As compared with CK, plant height and P_n significantly decreased with of the level of FLU and B[a]P treatments. Chlorophyll content increased at lower concentrations but declined at higher concentrations. Overall, the reduced vitamin C was inhibited by FLU; it was lowest at 5.0 mg·kg^-1 of FLU. The reduced vitamin C varied irregularly with B[a]P treatments; it increased slightly at 0.5 mg·kg^-1of B[a]P and was lowest at 5.0 mg·kg^-1 of B[a]P, compared with CK.

Aims Weed communities in rape fields have changed with occurrence of extreme weather events and global warming. Our objective was to investigate the effects of different regimes of temperature change on rape (Brassica napus ‘Qinyou-10’) and eight companion weeds, i.e. Descurainia sophia, Euphorbia helioscopia, Avena fatua, Polypogon fugax, Veronica didyma, Alopecurus aequalis, Chenopodium glaucum and Amaranthus retroflexus, to help with predicting the succession of companion weed communities under extreme temperatures.
Methods Seed germination, seedling growth and several physiological properties were investigated under five temperature treatments (10 °C/5 °C, 18 °C /10 °C, 25 °C /20 °C, 35 °C /30 °C and 40 °C /35 °C) (day/night) controlled by a climate-control growth chamber. Physiological properties tested included contents of malondialdehyde (MDA), soluble sugar and soluble protein, and activities of superoxide dismutase (SOD) and peroxidase (POD).
Important findings There were significant differences among the weed species in response to temperature change. The optimal temperatures for seed germination in Alopecurus aequalis, Chenopodium glaucum and Amaranthus retroflexus were high; for instance, the highest seed germination rate (91%) occurred at temperature of 40 °C /35 °C in Amaranthus retroflexus. In contrast, seed germination in Descurainia sophia, Euphorbia helioscopia, Avena fatua, Polypogon fugax and Veronica didyma required a much lower optimal temperature (i.e. 10-18 °C). At the highest treatment temperature (40 °C /35 °C), Amaranthus retroflexus seedlings grew vigorously, and their MDA contents were much lower than under low temperature treatment of 10 °C /5 °C. Moreover, the concentrations of soluble sugar and soluble protein and the activities of SOD and POD in Amaranthus retroflexus seedlings all increased with temperature, indicating the strong ability of this weed species in adapting to high temperature stress. Chenopodium glaucum had the similar responses as Amaranthus retroflexus in those properties to changes in temperature. Therefore, these two weeds should be paid more attention with the increasingly intensified global warming. Contrarily, at the lowest treatment temperature of 10 °C/5 °C, seed germination reached 100%, and the seedlings exhibited high soluble sugar and soluble protein concentrations as well as high SOD and POD activities in Avena fatua. Descurainia sophia had the similar responses as Avena fatua. Therefore, we should take additional measures to prevent malignant growth of Avena fatua and Descurainia sophia in cold years. Rape (‘Qinyou-10’) had stable and high seed germination rate, and grew well as seedlings, indicating that it better adapted to temperature changes compared to the eight companion weeds. We deduced ‘Qinyou-10’ is a rape species that can adapt well to temperature changes.

Aims The radial growth in Picea meyeri is reportedly limited by different climatic factors at different elevations. Our objectives were to investigate the variations in the responses of radial growth to climate warming, and to determine the distribution pattern along elevational gradient in P. meyeri.
Methods We selected four sites representing a range of elevations on the southern slope of Luya Mountain in Shanxi Province, and took increment core samples from trees on each site for establishing tree-ring width chronologies along the elevational gradient. Statistical characteristics were computed in order to assess the reliability of the chronologies. Inter-chronology correlation was conducted to determine the growth trends during 1958-1983 and 1984-2007. Person’s correlation was also performed to investigate the relationships between tree growth and climate. At last, the dynamics of growth-climate relationship were analyzed with the moving correlation method to examine the variations of dendroclimatic in response to climate warming.
Important findings At the lower elevations, there was a stronger influence of climate on tree growth in P. meyeri during the period 1984-2007 with increasing temperature than during 1958-1983 with decreasing temperature; whereas the growth of trees displayed reversed patterns of climate effect between the two periods at higher elevations. The growth and climate relationship in P. meyeri varied with elevations. At 2 060 m a.s.l., the significance level of the relationship between tree growth and July precipitation increased from p < 0.05 during 1958-1983 to p < 0.01 during 1984-2007; a significant negative correlation (p < 0.05) was found between the tree growth and the monthly mean temperature in May-July. At 2 330 m a.s.l., the tree growth showed a highly significant positive correlation (p < 0.01) with July precipitation during 1958-1983, but was not significantly related to any of the climate factors during 1984-2007. In contrast, the growth of trees did not show any significant relationship with climate during 1958-1983 at 2 440 m a.s.l., but it was found to be significantly (p < 0.05) and negatively correlated with monthly mean temperature in October of the previous season during 1984-2007. At 2 540 m a.s.l., there was a highly significant (p < 0.01) negative correlation between the tree growth in P. meyeri and the mean temperature in November of the previous season during 1958-1983, and significant (p < 0.05) negative correlations were found between the tree growth and monthly mean temperatures in October of the previous season and January of the current season, as well as between the tree growth and the monthly precipitation in June during 1984-2007. According to the moving correlation analysis, with increasing temperature, the influence of main climate factors on growth enhanced at lower elevations whereas weakened at higher elevations, which probably explain the reduced sensitivity of growth response to climate warming at higher elevations in P. meyeri. Our study suggests that climate warming would alter the difference in the relationship between and climate factors caused by elevation gradient in P. meyeri.

In order to understand the mechanisms in the responses of grassland ecosystems to global warming, this paper overviews the principle, the warming effect, and the advantages and disadvantages of infrared heating techniques. Recent advancement in research on the responses of grassland ecosystems to climate warming by using infrared heating techniques is reviewed, which covers the areas of plant phenology, photosynthetic physiology, growth and development, community structure and function, and soil characteristics, especially underground processes of plant communities. The key future research needs on the responses of grassland ecosystems to global warming are suggested.