Aims Phenology refers to periodic appearances of life-cycle events. It is crucial for predicting plant phenological responses to climate change and for identifying the period of carbon-uptake. Tracking the real-time canopy status accurately, especially in harsh environments, is becoming a large challenge for understanding and modeling vegetation-climate interactions. Our objective focuses on how to obtain relatively accurate real-time canopy status in Qinghai-Xizang Plateau using digital camera images.
Methods A standard, commercially available webcam was mounted at the top of the eddy covariance tower at the Damxung Rangeland Station. Images were collected every half an hour from 9:30 a.m. to 5:00 p.m. local time each day. We extracted red, green, and blue color channel brightness data for a region-of-interest (ROI) from each image (ROI, the subset of image, can better describe the target’s characters). The size of ROI is [100:180] and [10:380]), and it composed the different greenness indices according to the equations. We confirmed the best one that can reflect the size of leaf area index and variations in chlorophyll content by comparing different indices.
Important findings The absolute greenness index (2G_RB) is able to describe the canopy status qualitatively and quantitatively and is powerful in tracking community phenological stages. This indicates that digital cameras can be used in monitoring real-time phenology of alpine grassland community. Linear regression analysis of soil moisture indicates greenness is best explained by surface soil moisture (≤10 cm). By comparing canopy phenological events with conventional meteorological data, we also speculate that precipitation plays a critical role in triggering the spring phenological response in semiarid alpine grassland.

Aims Plant leaf stoichiometry plays critical roles in the photosynthesis rate, growth rate, dynamics of food chains and biogeochemical cycles. Although previous research showed that nitrogen has a scaling relationship with phosphorus, the relationship between elements besides nitrogen and phosphorus rarely have been studied. This project was to explore the scaling relationships between leaf elements (i.e., Fe, Ca, P, N, S, K) at an arid-hot valley.
Methods Leaf samples were collected from 51 plots located 1000-1400 m above sea level in the arid-hot valley of Jinsha River. Biomass in plots was sorted by species and measured. Leaf elemental contents of 107 samples were qualified. Relationships among these biogenetic elements were analyzed by standard major axis at both plot and individual levels.
Important findings There were always positive scaling relationships between studied elements when they were significantly correlated. The power law exponents derived from log-log scaling relations were near 2/3 for nitrogen relative to phosphorus at the plot level. The power law exponents for iron to N, P, K were >2 at the individual level. The rank of increasing rate in scaling relationships was Fe > Ca > P > N > S > K at the individual level. However, it was Fe > Ca > P > S > K > N at the plot level. We found that iron might be an important element in plant growth in the arid-hot valley for the higher increasing rate of investment in iron versus other elements. The differences in scaling relationships among elemental concentrations between the individual and plot levels suggest that community assembly process has an important role in determining plant stoichiometry at different levels of organization.

Aims Our objective is to study the variation in floral traits of Saussurea stella in 20 populations in response to elevation and mean plant size on the East Qinghai-Xizang Plateau.
Methods We used population means to evaluate sources of variation in reproductive allocation within species. In addition, we used the sample investigation method and dry weight to evaluate biomass.
Important findings Reproductive allocation is negatively correlated with mean plant size. There are trade-offs of resource allocation in reproductive biomass and vegetative biomass, capitulum number and its weight, male and female as well as filament and pollen. Additionally, there is a relationship between variation in floral traits of S. stella and elevation. Consequently, the variation of floral traits ensures that S. stella pollinates effectively and completes sexual reproduction.

Aims Our objectives were to analyze the geographic distribution characteristics of four critically endangered species of Abies in China’s subtropical regions, clarify their relationship with climatic conditions and determine the climatic factors that restrict the geographic distributions.
Methods Geographic distribution information was collected from field survey and literature materials. Climate information was collected from China’s meteorological stations and used to build a climate database of the distribution area. Commonly used climatic indexes and research methods were applied to analyze the relationship between geographic distribution and climate. Restrictive climatic factors were determined based on factor analysis.
Important findings Abies beshanzuensis, A. fanjingshanensis, A. yuanbaoshanensis and A. beshanzuensis var. ziyuanensis are scattered in the subtropical region of China. The horizontal range of distribution is narrow: 25°25′-27°55′ N, 108°42′-119°12′ E. The populations are distributed vertically in the upper part of mountains, with altitude ranging from 1363 to 2390 m. The uppermost altitude rises with decreasing longitude. Temperature of the entire distribution area is low, with mean annual temperature 7.4-11.2 °C. Precipitation is abundant, with a mean annual precipitation of 1265-1946 mm, of which 75% falls in the growing season. Humidity is high, and annual relative humidity reaches 77%-86%. The ranges of climatic indexes are narrow, indicating specific requirements for water and heat. The coldness index of the distribution area is low, limiting vertical diffusion towards low altitude. Therefore, the populations are confined in the upper part of mountains. The distribution areas of different species share similar climatic conditions. The temperature is relatively lower in the distribution area of A. fanjingshanensis. The humidity is slightly higher in the distribution area of A. yuanbaoshanensis. Three climatic factors have a significant impact on geographic distribution. The ranking is low temperature factor > extreme low temperature factor > humidity factor. Considering global warming, suitable habitats of these four critically endangered species will continue to decrease until extinction of the species, so we urgently need to carry out immediate ex-situ conservation.

Aims Mycorrhizae, as the symbiotic associations between plant roots and mycorrhizal fungi, are almost ubiquitous. Mycorrhizal fungi play a crucial role in the regulation of terrestrial net primary production carbon dioxide (CO₂) fluxes and respond strongly to climatic changes in temperature. Our objective was to explore how interannual variations in air temperature influence net primary productivity (NPP) in global forest ecosystems that are classified by the mycorrhizae of the dominant plants.
Methods A new database was established including NPP and mean annual air temperature (MAT) of forests dominated by different mycorrhizal strategies based on an existing global forest database. We used this new database to study the responses of NPP of forests dominated by different mycorrhizal strategies to air temperature change.
Important findings Total NPP, aboveground NPP and belowground NPP increased with the increase of MAT, although the slopes were different in forests dominated by different mycorrhizal types. Total NPP increased with the rise of MAT in forests dominated by all mycorrhizal strategies out of arbuscular mycorrhiza (AM) and AM + ectomycorrhiza (ECM) + ectendomycorrhiza (EEM). The responses of above- and below-ground NPP of forests to the variation of MAT changed depending on mycorrhizal strategies of dominate forest tree species. The MAT explained 57.27% of the variation of aboveground NPP in AM + ECM forest. Significant regressions between belowground NPP and MAT were observed in ECM and ECM + EEM forests. NPP values of main stem, tree leaf and fine root tended to either increase or decrease with the increase of MAT in the different forests. As far as the comparison between AM and ECM forest was concerned, the NPP, including total NPP and each part, was more sensitive to air temperature change in forest dominated by ECM than forest dominated by AM. We conclude that different mycorrhizae affected the responses of forest NPP to air temperature change by influencing the extent of response of various parts of forest NPP to air temperature change. The mycorrhizal symbiosis makes this vital for accurate prediction of future changes of forest NPP with change of air temperature.

Aims Previous studies discovered unusual plasticity in root growth of Callistephus chinensis, in that fewer fine roots grow in pulse soil nutrient patches than in unfertilized patches. Our goal is to interpret this event via experimentation following the theory of plant physiological ecology. The experiment tested the following hypotheses: NO₃ ^-, NH₄ ⁺ and method of application 1) significantly affect root growth and 2) significantly affect root hormones and 3) root hormones (auxin (IAA), abscisic acid (ABA), and cytokinin (zeatin riboside + zeatin) (CK (ZR + Z))) significantly affect root architecture (indicated by the length of the 1st order fine roots, the inter 1st order root length and the density of the 1st order fine lateral roots).
Methods The water culture approach was employed with treatments of two fertilizers (NO₃ ^-and NH₄ ⁺), two methods of application (stable vs. pulse, i.e., pulse shift to high N concentration from low and mid concentration) and low, mid and high concentrations of the fertilizers (NO₃ ^-: 0.2, 1.0 and 18.0 mmol·L ^-1; NH₄ ⁺: 0.2, 4.0 and 20.0 mmol·L ^-1). The experiment lasted 35 days after the treatments, the plants were harvested by the end of the experiment and all concerned parameters were measured including root mass, the above-mentioned root architecture parameters and the contents of root hormones.
Important findings The experimental treatments affected root mass and root hormones with different significances. The high concentrations of NO₃ ^- and NH₄ ⁺ both greatly lowered the root mass and IAA. Values were lower in the NH₄ ⁺ culture than in the NO₃ ^- one. Pulse shift treatment lowered both further. CK (ZR + Z) contents did not respond to the concentrations and the methods of application, but to NO₃ ^- or NH₄ ⁺; the latter led much lower CK (ZR + Z) contents than the former. Root mass had positive regression relationships with 1st order root length and the density of the fine lateral roots, had a linear regression relationship with IAA, a negative exponential relationship with CK (ZR + Z) and complicated relationships with ABA. The different hormones had different relationships with the root architecture parameters. They were all irrelevant with 1st order inter-root length, ABA had relationships with 1st order lateral root density only and IAA and CK (ZR + Z) both had significant regression relationships with 1st order root length and 1st order lateral root density. The results established physio-ecological path relationships of heterogeneous nutrient stimulation→changes in root hormone contents→changes in root architecture→root plastic growth. As to the unusual root growth of C. chinensis, we infer that the species had very low tolerance to temporal variation in the N environment, particularly NH₄ ⁺.

In order to effectively absorb nutrients from naturally heterogeneous soil, plant roots employ various plastic responses to the environment heterogeneity through evolution and adaptation. In addition, plant roots also face competition from both intra- and inter-specific competitors. Factors affecting the outputs of root competition include nutrient availability, scale and degree of soil heterogeneity and ability of root plasticity. Competition adds a new dimension to plants; plant roots may alter their normal plastic responses, e.g., root competition will affect the spatial distribution of root systems. Different plastic responses of roots will in turn influence root competition per se. Previous studies have revealed that plants with high root morphological plasticity and high physiological plasticity achieved competitive advantages. Plants differ in their root nutrient foraging plasticity, and therefore may not have fixed ways of responding to competition. The uniqueness and traits of species need to be considered in comprehending the mechanisms of their plastic responses of root foraging in competition and the consequences. The responses of roots to competitors may also be influenced by the competitors, and the competitive status of the plant may change. Closely related plants may be more likely to avoid the competition from each other. A few studies have focused on integration of root competition and root foraging plasticity, as well as the impact of root competition on the community structure. This review is intended to discuss this issue.

Litter decomposition is one of the most important and dynamic components of nutrient cycling in ecosystems. In addition to the well-known actions of plant roots on litter, roots also constitute an important biotic factor regulating litter decomposition. However, relatively little attention has been given to this. Relative to the upper litter layer, the middle and lower layers are enriched in water and nutrients, which provide favorable conditions for root growth. By proliferating in litter, roots potentially influence litter decomposition through a priming effect, mycorrhizal fungi and N uptake. We give an overview of root foraging in litter, including factors influencing it. We then review its influence and possible mechanisms of root growth on litter decomposition. We also propose a conceptual module that enhances understanding of the relationship between root and litter decomposition.

Nitrogen (N), phosphorus (P) and their stoichiometry play pivotal roles in plant structure and functions, development and ecological strategies in terrestrial ecosystems due to their coupling with each other and their irreplaceability. Plant N and P can be influenced by biotic and abiotic factors, such as individual traits, climate change and human disturbance, and it is those factors that determine the plant community composition and structure that finally affect the ecosystem processes. According to previous studies, there is an allometric relationship between N and P. Relationships between plant N and P depend on the soil nutrient condition and species plasticity in N and P. Understanding the relationships between plant N and P in major ecological gradients can further our knowledge about vegetation restoration, succession, biodiversity, ecosystem trophic structure and biogeochemical cycles. This information could help predict potential changes in terrestrial ecosystems in response to future climate change. We review recent advances in the influencing factors and mechanism of stoichiometry in order to improve understanding of plant responses to global change.