Soil carbon and sugars play key roles in carbon (C) cycling in grassland ecosystems. However, little is known about their changes in quantity and composition in degraded alpine meadows in the Tibetan plateau. We compared vegetation C density, soil organic carbon (SOC) density, and soil sugars in nondegraded (ND), degraded (DA; following artificial restoration), and extremely degraded (ED) grasslands and analyzed the relation among these parameters by redundancy analysis (RDA) and structural equation models (SEMs). Belowground biomass, soil microbial biomass C, soil microbial biomass nitrogen (N), belowground biomass C density, SOC density, and soil sugars were lower in DA and ED grasslands than in ND grasslands. In addition, the ratio of belowground biomass to aboveground biomass (BAR) decreased with an increase in degradation. The ratio of belowground biomass to aboveground biomass was identified as the main indirect driving force of ecosystem C density by affecting total vegetation C and SOC densities. Soil dissolved organic carbon (DOC), microbial biomass carbon (SMBC), neutral sugars (NS), and total nitrogen (TN) were identified as main direct driving forces. The ratio of belowground biomass to aboveground biomass altered DOC, SMBC, NS, and TN and, consequently, was the primary driving force for the alpine meadows’ ecosystem C density. It was concluded that land management in alpine meadows should include practices that maintain a relatively high BAR in order to curb degradation and increase ecosystem C density.

AIMS: We assessed and quantified the cumulative impact of 20 years of biomass management on the nature and bioavailability of soil phosphorus (P) accumulated from antecedent fertiliser inputs. METHODS: Soil (0–2.5, 2.5–5, 5–10 cm) and plant samples were taken from replicate plots in a grassland field experiment maintained for 20 years under contrasting plant biomass regimen- biomass retained or removed after mowing. Analyses included dry matter production and P uptake, root biomass, total soil carbon (C), total nitrogen (N), total P, soil P fractionation, and ³¹P NMR spectroscopy. RESULTS: Contemporary plant production and P uptake were over 2-fold higher for the biomass retained compared with the biomass removed regimes. Soil C, total P, soluble and labile forms of inorganic and organic soil P were significantly higher under biomass retention than removal. CONCLUSIONS: Reserves of soluble and labile inorganic P in soil were significantly depleted in response to continued long-term removal of P in plant biomass compared to retention. However, this was only sufficient to sustain plant production at half the level observed for the biomass retention after 20 years, which was partly attributed to limited mobilisation of organic P in response to P removal.

Plant species may exert a strong influence on soil biological properties, but the linkages between plant and soil responses to severe drought remain unclear. We conducted an outdoor mesocosm experiment with five upland grass species and one Mediterranean drought-resistant grass cultivar to investigate the effects of root biomass and rhizosphere conditions on the drought responses of soil microbial biomass in the topsoil. In particular, we assessed whether variation in the drought resistance of microbial biomass could be linked to root biomass, soil inorganic nitrogen (N) or dissolved organic carbon (DOC). Experimental drought decreased microbial biomass but increased soil inorganic N and DOC across plant species. Root biomass responses to drought were less predictable, and varied depending on species. Microbial biomass resistance to drought showed a negative relationship with the drought resistance of root biomass across species, possibly via changes in rhizodeposition. Moreover, the drought resistance of microbial biomass showed a negative relationship with soil nutrient availability under droughted conditions. Our findings highlight the importance of root biomass as a predictor of soil microbial resistance to drought in grass-dominated systems, and suggest that trade-offs between plant and microbial processes could have significant implications for ecosystem function in a changing environment.

Background: In ecosystem carbon cycle studies, distinguishing between CO2 emitted by roots and by microbes remains very difficult because it is mixed before being released into the atmosphere. Currently, no method for quantifying root and microbial respiration is effective. Therefore, this study investigated the relationship between soil respiration and underground root biomass at varying distances from the tree and tested possibilities for measuring root and microbial respiration. Methods: Soil respiration was measured by the closed chamber method, in which acrylic collars were placed at regular intervals from the tree base. Measurements were made irregularly during one season, including high temperatures in summer and low temperatures in autumn; the soil’s temperature and moisture content were also collected. After measurements, roots of each plot were collected, and their dry matter biomass measured to analyze relationships between root biomass and soil respiration. Results: Apart from root biomass, which affects soil’s temperature and moisture, no other factors affecting soil respiration showed significant differences between measuring points. At each point, soil respiration showed clear seasonal variations and high exponential correlation with increasing soil temperatures. The root biomass decreased exponentially with increasing distance from the tree. The rate of soil respiration was also highly correlated exponentially with root biomass. Based on these results, the average rate of root respiration in the soil was estimated to be 34.4% (26.6~43.1%). Conclusions: In this study, attempts were made to differentiate the root respiration rate by analyzing the distribution of root biomass and resulting changes in soil respiration. As distance from the tree increased, root biomass and soil respiration values were shown to strongly decrease exponentially. Root biomass increased logarithmically with increases in soil respiration. In addition, soil respiration and underground root biomass were logarithmically related; the calculated root-breathing rate was around 44%. This study method is applicable for determining root and microbial respiration in forest ecosystem carbon cycle research. However, more data should be collected on the distribution of root biomass and the correlated soil respiration.

We studied the impacts of light availability and soil flooding on biomass accumulation and tissue biomass fractions in Lindera melissifolia (Walt.) Blume, an endangered woody shrub of the southeastern United States. Our experiment was located in a large-scale flooding research facility where plants were established and grown for three years while receiving combinations of 70%, 37%, or 5% of full sunlight with either 0, 45, or 90 days of soil flooding. We hypothesized that biomass accumulation would decrease with decreasing light availability and that soil flooding would further reduce plant mass. In the absence of soil flooding, shrubs receiving 37% light accumulated the greatest biomass (972 g), shrubs receiving 70% light were intermediate in biomass accumulation (737 g), and shrubs receiving 5% light accumulated the least biomass (14 g). Shrubs raised beneath 37% light had root biomass fractions less indicative of water stress than shrubs raised beneath 70% light, and leaf and stem biomass fractions less indicative of light deprivation than shrubs raised beneath 5% light. The light environment also influenced how soil flooding affected L. melissifolia biomass accumulation. Soil flooding had no detectable effect on the amount of biomass accumulated by shrubs acclimated to 5% light. However, shrubs acclimated to 70% or 37% light showed a 26% decrease in biomass accumulation after 90 days of soil flooding. Our findings demonstrate a responsive plasticity of L. melissifolia biomass accumulation relative to light availability and soil flooding, and this plasticity was driven by shifts among leaf, stem, and root biomass fractions. This plasticity supports development of silvicultural options for active management of this endangered species in floodplain forests of the Mississippi Alluvial Valley.

Winter snowfall is an important source of moisture that may influence the growth and development of biological soil crusts (BSCs) in temperate desert regions of China. Yet there is still limited empirical knowledge about the effect of snowfall on BSCs. In this study, moss crusts from the Gurbantunggut Desert were exposed to five snow depths to evaluate how snowfall affected the physical–chemical properties (pH; electric conductivity, EC; soil organic carbon, SOC; total nitrogen, TN; available nitrogen, AN; available phosphorus, AP; available potassium, AK) and microbial biomass (soil microbial biomass carbon, SMBC; soil microbial biomass nitrogen, SMBN; soil microbial biomass phosphorus, SMBP) of soil in the BSCs, before (in October 2016: representing three consecutive years of snow manipulation) and after winter (in April 2017). Results showed that the soil water content increased significantly as snowfall depth increased (p < 0.05) in October 2016 and April 2017. Most of the soil physical–chemical features (EC, SOC, TN, AN, AP, and AK) and microbial biomass (SMBC and SMBN) showed an increase with an increase of snowfall depth after three consecutive years of snow manipulation. Moreover, for most experimental treatments, after a winter of melting snow (in April 2017) most of the soil properties were significantly higher (p < 0.05) than found in October 2016. Together, these results showed that the dynamics of soil nutrients and microbial biomass in moss BSCs were affected by snowfall depth in Gurbantunggut Desert. Different snowfall depths can have different effects on the dynamics of soil nutrients and microbial biomass of moss crusts, an impact that may alter the future growth and development of BSCs. Thus, we suggest that the potential influence of snowfall depth on soil nutrients and microbial biomass dynamics in BSCs require consideration when discussing the effects of moisture on ecological functions of BSCs in arid and semi–arid regions.