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Location: Home > Research Areas > Soil Nutrient Cycling and Control Mechanisms
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Ecological stoichiometry and soil C and N cycling
 

Stoichiometric homeostasis in ecosystem structure and functioning

Nitrogen is an essential element for living organisms. The productivity of plants and soil microbes largely depends on N availability, which imposes stoichiometric constraints on individual organisms. A tight coupling of terrestrial N and C cycles in ecosystems and their components usually maintains a relatively stable ratio of C:N. Evidence is accumulating that N availability plays an important role in mediating the productivity, structure and spatio-temporal dynamics of terrestrial ecosystems. Our research in the temperate steppe further demonstrated that homeostasis of C:N:P plays an important role in regulating community structure and ecosystem function (Yu et al. 2010). Based on comprehensive studies in the grasslands of Inner Mongolia, we found that species-level stoichiometric homoeostasis consistently displayed a positive correlation with dominance of species and ecosystem stability across large spatial and temporal scales. At the community level, stoichiometric homoeostasis was also positively correlated with ecosystem function and stability. Thus homoeostatic species tend to have high and stable biomass; and ecosystems dominated by more homoeostatic species have higher productivity and greater stability. This study demonstrates the relationship between stoichiometric homeostasis and ecosystem structure and functioning, and reveals a new mechanism for the sustainability of ecosystems.

Figure 19: Relationships between the index of stoichiometric homeostasis (H) and the dominance of species and community stability (A: N addition experiment; B: 27-yr monitoring study; C: 1200-km transect).

C:N:P ratio as an indicator of effects of global climate change on C-N cycling

Shifts in the C:N:P ratio of plants control several processes of ecosystem C and N cycling. Nutrient resorption during the senescence of plant tissues affects the nutrient quality of litter and consequently influences litter decomposition. C:N:P and nutrient resorption of plants are sensitive to global climate change. Their responses would also be affected by ecosystem management strategies, and subsequently generate feedback to ecosystem C and N cycling. In the past three years, we have focused on the responses of plant stoichiometry to global climate change and ecosystem management strategies in the temperate steppe of northern China. We have found that: (1) There is a positive feedback between plant litter quality and soil nutrient status even at the micro-scale (1 m) as mediated by changes in plant nutrient resorption, indicating the important role of plasticity of plant nutrient use strategies in driving ecosystem nutrient cycling (Lü et al. 2012a); (2) N deposition stimulates the uptake and turnover of P in ecosystems. Convergent responses of N and P resorption to N deposition demonstrates the importance of nutrient resorption as a pathway through which plants and ecosystems adjust in the face of increasing N availability (Lü et al. 2013); (3) The impacts of N deposition on plant stoichiometric ratios will depend on water availability, indicating strong interactions among different global change factors on plant physiological traits (Lü et al. 2012b); (4) Ecosystem management strategies, such as mowing (Lü et al. 2012c) and prescribed fire (Lü et al. 2011) also influence the effects of N deposition on ecosystem and plant stoichiometric traits. Together these studies reveal that shifts of plant stoichiometric ratios are an important pathway through which global climate change factors affect ecosystem C and nutrient cycling.

 

Figure 20: C:N:P ratio mediated the effects of global climate change and ecosystem management strategies on ecological processes.







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