Epichloë infection can affect the intraspecific and interspecific competitive ability of the host plants. However, few studies have been reported on the effects of endophyte infection on the diversity and productivity of host communities.

We used endophyte-infected (E+) and uninfected (E-) Achnatherum sibiricum, plus five other common species in its native community to construct a microcosm plant community to investigate the community-level consequences of endophyte interactions under different nutrient and mowing treatments.

Community-level consequences of endophyte infection depend on the mowing treatment. Endophyte infection did not alter plant community diversity under non-mowing conditions. Under mowing conditions, however, endophyte infection significantly increased the diversity by increasing the abundance of lower abundance species such as Agropyron cristatum and Stipa grandis, while decreasing the abundance of dominant species such as Leymus chinensis. No significant endophyte effect on the productivity of plant community was found. With respect to nutrient treatments, we found that nutrient addition had no significant effect either on the diversity or productivity of the plant community. The positive effect of endophyte on A. sibiricum occurred only under nutrient addition treatment in the host species level.

Exploring the relationship between biodiversity and ecosystem productivity has become a hot topic in ecological research. The results support the mass ratio hypothesis and niche complementarity hypothesis, but their relative importance is still controversial. Our aim is to test the relative importance of these two hypotheses in explaining the variability of productivity, and to explore whether the relationship between biodiversity and productivity is influenced by both biotic and abiotic factors.

We used the data of woody plants in a 9 hm² typical mixed broadleaved-Korean pine forest. By calculating the initial biomass, species diversity, functional diversity, community-weighted mean functional traits and measuring environmental factors, we analyzed the relationship between diversity and productivity by the linear regression model and structural equation model.

The results showed that: (1) Both species diversity and functional diversity played a significant role in productivity, and functional diversity was more closely related to productivity than species diversity; (2) the functional diversity index could better explain the variation of productivity than community-weighted mean functional traits. It suggested that the niche complementarity hypothesis was more suitable for explaining the variation of productivity in the mixed broadleaved-Korean pine forest; (3) the relationship between biodiversity and productivity was affected by biotic and abiotic factors, and compared with diversity and functional character composition (vegetation quality), initial stand biomass (vegetation quantity) could explain the variation of productivity more effectively. Our study suggests that, it is important to maintain forest functional diversity and strengthen the protection of plants and soil environments to increase productivity and biodiversity effectively.

Litters of emergent plants are important components of material cycling in wetland ecosystems. To clarify the effects of climate warming and habitat difference on the litter decomposition processes and phyllospheric microorganisms of wetland emergent plants is of great significance for revealing the key material cycling processes in wetland ecosystems.

Zizania latifolia, a dominant emergent plant in typical wetlands of Northwestern Yunnan Plateau, was chosen for this study. Using litter bag methods, we studied mass remaining and the abundance, community structure and metabolic potential of phyllospheric microorganisms of the litter from Zizania latifolia under simulated warming (1.5-2.0 ℃) and under three habitats (air, water and soil interface).

Simulated climatic warming and habitat difference significantly affected the litter decomposition rate. After one-year decomposition, the mass remaining of litter was 66.4% under the simulated warming treatment, while 77.7% under the control treatment. The decomposition constant (k) value was 1.64 times under warming compared to the control. The mass remaining of litter at the water and soil interface was 42.2% and 25.3%, and the k value at the water and soil interface was 3.63 and 5.25 times of that at the air interface respectively. These results indicate that habitat difference was the key factor controlling the decomposition of emergent plant litter in wetlands. Moreover, warming mainly changed the community composition of litter phyllospheric microorganisms, while decomposition interface mainly affected the abundance, community structure and metabolic potential of phyllospheric microorganisms. Notably, phyllospheric microorganisms of litter at soil interface had the highest metabolic potential and utilized alcohols as main carbon sources. The characteristics of phyllospheric microorganisms between different treatments were in good agreement with litter decomposition rate, which provides an important theoretical basis for revealing the microbial mechanisms driving the decomposition of wetland plant litter.

Understanding the differences in root architectural strategies among the species and the differences in morphological characteristics among different root orders will facilitate our understanding root growth and development strategies, and thus provide a basis for predicting and modeling the root systems for mature trees. In this study, we analyzed the morphological characteristics and topological relationships for the root systems of two Populus tomentosa trees and one Robinia pseudoacacia tree.

A method combining both excavation and analysis was applied to extract and quantify root architectural characteristics of the three root systems. The morphological characteristics such as root basal diameter, root length, link length, and root number of different root orders were described using the developmental analysis method of Rose (1983), and their topological relationships were analyzed.

1) The modified topological indices q_a and q_b were close to 0, and the topological index TI was close to 0.5 for all three root systems, indicating their dichotomous structure. The depth and width of the systems ranged from 5.7 to 6.4 m and from 7.6 to 13.5 m, respectively. Root grafts occurred in the same species. 2) The root systems could have the seventh or eighth order roots. The basal root diameter and root length significantly decreased with increasing root order. The first order roots had 5.79-36.92 times the basal diameter and 1.45-9.11 times the length of higher order roots. With increasing root order, the root number increased, and reached a maximum value for the third order roots, and then decreased. 3) In roots of each of the first three orders, the link length varied little from the root base towards its tip, indicating that the child roots were distributed evenly on their parent roots and thus help trees absorb soil resources more efficiently. 4) The regression of basal diameters of child roots on basal diameters of their mother roots showed that the smallest slope for the first order roots (average slope 0.15) and no big difference in the slope between the second and third order roots (0.34 versus 0.35). This suggested that the first order roots developed their own diameter first for anchoring and supporting the tree, while the second and third order roots developed their child roots to facilitate nutrient uptake from the soil. 5) The regression of root length on root basal diameter suggested that the slope increased from 10.46 to 90.43 with increasing root order, which implies that the higher order roots tended to develop their length to explore resources and expand their space.

The conduits characters are critical for plants to develop their survival strategies. Our current knowledge in this regard remains limited for the subtropical forest. In this study, we set a study objective to quantify the relationship between the conduits characters and the leaf functional traits of the dominant species in the region.

Two dominant species, Castanopsis chinensis and Schima superba, in a subtropical forest in Shimentai Nature Reserve were selected to compare their differences in functional traits, including conduits anatomical structure, the leaf morphological characteristics, and leaf physiological characteristics. The study was conducted during the dry season (October to March of the following year) for quantifying the ring-porous and diffuse-porous species. A series of t-tests were performed to quantify the statistical differences of all traits between the two species.

We found that the density of conduits of S. superba (diffuse-porous) was significantly higher than that of C. chinensis (ring-porous), while the diameter of conduits for C. chinensis was much larger than that of S. superba. The leaf water content and the Chlorophyll a/Chlorophyll b ratio were much higher for S. superba than that of C. chinensis; the stomatal density and specific leaf area (SLA) tended to be higher in C. chinensis. In addition, it appeared that the differences in leaf specific net photosynthetic rates and the leaf stomatal conductance were not significant between S. superba and C. chinensis. These results indicated that the ring-porous species C. chinensis maintain a high photosynthetic capacity by maintaining a higher SLA at the expense of low leaf water content in responding to the water stress. The diffuse-porous species S. superba, meanwhile, tended to maintain a high capability of light transform under drought. These functional differences might be responsible for the succession pathways under the gradual changes of global precipitation for the region.

Hormones are important signals for plants adaption to environmental stresses. To understand the mechanism of plants adaptation to nutrient deficiency from the perspective of hormone regulation is of great significance for breeding the genotypes with high phosphorus (P)-use efficiency.

This study investigated the correlation between hormone content and the adaptability of Chinese fir (Cunninghamia lanceolata) to low P stress by examining the changes of hormone content, root morphology, root dry matter and root P distribution patterns in the passive tolerance (M1) and active activation (M4) genotypes under low P stress at different treatment periods.

No correlation was found between the foliar hormone contents and the adaptive characteristics of M1 and M4 under low P stress, although the root hormone content was significantly correlated with the growth index of roots. Low P stresses increased root IAA contents in M1 and M4 after 27 h of treatments and increased continuously with the prolongation of time. The IAA contents were positively correlated with surface area, volume and length of roots in both M1 and M4 (p < 0.05), suggesting that the increase of IAA induced root growth in both genotypes. Specifically, we observed an obvious phenomenon of IAA transportation from leaves to roots in M4, along with stronger root growth of M4 compared with that of M1. Meanwhile, low P stress increased the root-shoot ratio of M4, suggesting that root growth prompted more dry matter distribution to roots. Similarly, the ABA and GA₃ contents in both M1 and M4 roots also increased as P availability decreased, but they showed a trend toward decrease over time and a negative correlation with root growth. The ZT contents in the root lower under low P treatment, yet there was no significant correlation between its contents and the low P adaptive characteristics of M1 and M4. Our results indicated that the contents of root IAA, ABA, and GA₃ in Chinese fir clones with high P-use efficiency were closely related to the morphological changes of the roots. These comprehensive regulations of different organs is an essential survival strategy for plants to adapt to low P stress.

Soil respiration plays an important role in carbon cycling in grassland ecosystems. However, the effects of collar size and buried depth during field measurement on soil respiration are rarely assessed.

We conducted a two-factor experiment to examine how soil collar depth (2 cm and 5 cm) and size (15 cm × 15 cm and 30 cm × 30 cm) affected the soil respiration (SR), post aboveground net primary productivity (post-ANPP), soil temperature (ST), and soil water content (SWC) in a semi-arid steppe.

The results showed that the deep-inserted soil collar (5 cm soil depth) decreased the soil respiration by 8.0%-9.7% compared with the shallow-inserted soil collar (2 cm soil depth). The large-sized soil collar (30 cm × 30 cm) decreased the soil respiration by 9.1%-10.8% compared with the small-sized soil collar (15 cm × 15 cm). We also found that the deep-inserted and large-sized soil collars had higher ST but lower SWC compared with the shallow-depth and small-sized soil collars. Structural equation model indicated that the lower respiration in the deep-inserted and large-sized soil collars was due to the lower post-ANPP, ST, and SWC. Overall, we found that the soil collar size and buried depth can substantially alter the magnitude of soil respiration by changing plant biomass, ST, and SWC. These findings suggest that the influences of collar size and buried depth on soil respiration should be considered for better estimation and modeling of soil CO₂ fluxes in terrestrial ecosystems.

Nutrient additions such as nitrogen and phosphorus are important strategies to improve the productivity of the grassland ecosystem. However, their effect on soil nitrous oxide (N₂O) emissions remains unclear.

A field study was conducted in an alpine grassland located in the north slope of Kunlun Mountains in Southern Xinjiang. Four treatments included nitrogen addition alone (N), phosphorus addition alone (P), mixture of nitrogen and phosphorus additions (N + P) and an unfertilized control (CK). Gas samples were collected and analyzed using the static chamber chromatography methodology during the 2017 growing season. Treatment effects on the characteristics of N₂O emissions from grassland soil were thoroughly investigated. Pearson correlation analysis was used to identify and quantify the influence of environmental variables on soil N₂O emissions.

The results showed that N and (N + P) treatments induced N₂O flux peaks after three weeks of fertilizer addition, with the maximum daily N₂O flux rates of 42.3 and 15.4 g N·hm ^-2·d ^-1, respectively. The N treatment significantly increased growing season cumulative N₂O emissions by 1.8 to 3.2 times compared to P treatment, (N + P) treatment and CK, and there were no significant differences between the three treatments. Pearson correlation analysis showed that daily N₂O flux rate was correlated negatively with soil microbial biomass carbon, and positively with soil pH and dissolved organic carbon. There was no significant correlation between daily N₂O flux rate and other environmental variables. These results suggest that simultaneous addition of nitrogen and phosphorus nutrients can significantly reduce soil N₂O emission compared to N treatment for the alpine grassland in this region.

The increase of atmospheric nitrogen (N) deposition caused by global change and industrial and agricultural production has had an important impact on the structure and function of ecosystems. There are many forms in composition of atmospheric N deposition. However, it is not clear whether there are differences in the effects of N deposition forms on structure and function of the ecosystems. Here our objective was to characterize the effects of different forms and levels of N addition on soil net N mineralization potential of steppe ecosystem in the Nei Mongol.

A N addition experiment was carried out in the meadow steppe in Nei Mongol using five different N fertilizers, including CO(NH₂)₂, NH₄HCO₃, NH₄NO₃, (NH₄)₂SO₄, and slow-release urea separately since 2014. There were six N addition levels with 0 (N0), 2 (N2), 5 (N5), 10 (N10), 20 (N20) and 50 (N50) g·m ^-2·a ^-1. Fresh soil samples from all treatments were taken and all roots were removed in July 2016. Then these soil samples were incubated for 24 h at 25 °C with 60% field water capacity. The potential of net N mineralization and nitrification rates and the potential of soil microbial respiration (MR), soil physical and chemical properties, soil microbial biomass carbon (MBC) and N (MBN) contents were measured, respectively.

The results showed that: (1) different forms and levels of N addition significantly increased soil inorganic N content and potential net N mineralization and nitrification rates. The N20 treatment had the highest soil inorganic N content and net N mineralization rate, however the highest soil net nitrification rate was found under N50 treatment; (2) different forms and levels of N addition significantly increased MBC and MBN contents and decreased the microbial metabolic quotient (qCO₂). Lower N addition (N2) enhanced MR, but medium and higher N addition (N20, N50) restrained the MR; (3) different forms and levels of N addition significantly reduced the soil pH value, but significantly increased the available phosphorus content. No effects were found in soil water content, total phosphorus, total N and soil organic carbon contents, separately. The results verified that soil available N was the limited factor affecting plant productivity in meadow steppe in Nei Mongol steppe. No matter what type of N fertilizer can increase the activity of soil microorganism and the potential net N mineralization rate of the meadow steppe in this area.