Effects of short‐term N addition on plant biomass allocation and C and N pools of the Sibiraea angustata scrub ecosystem

Abstract

Summary To explain the effects of short‐term N addition on plant biomass allocation and on carbon (C) and nitrogen (N) pools in an alpine scrub ecosystem, we carried out a field experiment in Sibiraea angustata scrubland on the eastern margin of the Qinghai‐Tibetan Plateau of China. After one and a half years of N addition at four rates (N0, control; N20, 20; N50, 50; N100, 100 kg N ha−1 year−1), we investigated the amount and allocation of biomass and the C and N pools in several parts of the ecosystem, including shrubs (leaves, shoots and branches, coarse roots and fine roots), grass (above‐ and below‐ground) and litter (wood and leaf debris) components, and seven depth intervals within the soil (0–5, 5–10, 10–20, 20–30, 30–50, 50–70 and 70–100 cm). The results were as follows: (i) total vegetation biomass showed a linear increase with the increase in N (P < 0.05), mainly from the increased root biomass in both shrubs and grasses, (ii) the ecosystem C and N storage were 36 and 3.26 kg m−2, respectively, of which the shrub, grass, litter and soil components contributed 11.08, 0.47, 0.25 and 88%, respectively, to the C pool and 3.07, 0.16, 0.08 and 97%, respectively, to the N pool, (iii) the ecosystem N pool did not change in response to the addition of N, whereas the ecosystem C pool responded linearly to increasing N (P < 0.05). These results suggest that the alpine scrub ecosystem functions as a net C sink under increasing atmospheric N deposition, mainly by promoting belowground C sequestration. Highlights Effects of short‐term N addition on biomass allocation and C and N pools in alpine scrub. Response to N addition in C pool of components of the ecosystem and soil at depth (0–100 cm). Root:shoot ratio of vegetation and ecosystem C pool increased linearly with increasing N. Alpine scrub ecosystem may function as a net C sink under increasing atmospheric N deposition.

Effects of N Addition Frequency and Quantity on Hydrocotyle vulgaris Growth and Greenhouse Gas Emissions from Wetland Microcosms

“…The results indicated that the growth of H. vulgaris benefited from sufficient nutrient conditions, which was consistent with previous findings [29]. Our results also confirmed that appropriate N addition can promote plant growth, thus increasing plant productivity [10].…”

“…N is an essential element for plant growth, and N-limitation can affect physiological activities and development [8,9]. N deposition can increase plant biomass and decrease the root-to-shoot ratio within a certain supply range [10]. An increase in N availability may facilitate the successful invasion of exotic plants into new plant communities [11].…”

“…N deposition alters CO 2 emission through an increase in plant biomass, a decrease in the C/N ratio of litter, and the mitigation of N restriction on microbial metabolism [12]. N deposition can affect CH 4 flux by altering the activity of methanogens and methanotrophs [3,13], affecting the allocation of plant biomass, and thereby the impact on CH 4 production, oxidation, and transport [10,14]. In addition, N deposition can increase N 2 O flux in wetlands because the growth and biomass accumulation of plants with N availability provide soil microorganisms with a more labile C source, which can be used as an energy source for denitrification [15,16].…”

Plants regulate the effects of experimental warming on the soil microbial community in an alpine scrub ecosystem

“…The alpine scrub ecosystem distributed on the Qinghai–Tibetan Plateau is among the most sensitive regions to climatic warming [ 1 ]. Occupying a total area of 1.06 × 10 5 km 2 , it is widely distributed across the transition zones between the alpine forest and grassland [ 18 ]. These alpine ecosystems play important roles in regulating C and nutrient cycling both regionally and globally [ 19 ].…”

“…Hence, the responses of the soil microbial community to warming in these alpine scrub ecosystems might be different than those in the alpine forest and grassland ecosystems, and the effects of climatic warming on soil microbial processes in these alpine regions are greatly uncertain. Previous studies that have examined the effects of environmental changes on the alpine scrub ecosystems of the Qinghai–Tibetan Plateau mainly focused on the effects of N addition on ecosystem C and N pools [ 18 ] and soil C fluxes [ 20 ]. So far, the responses of the soil microbial community structure and diversity to warming in these Qinghai–Tibetan Plateau alpine scrub ecosystems have received little attention.…”