Xinying Cheng

Effects of nutrient heterogeneity and competition on root architecture of spruce seedlings: implications for an essential feature of root foraging.

Background We have limited understanding of root foraging responses when plants were simultaneously exposed to nutrient heterogeneity and competition, and our goal was to determine whether and how plants integrate information about nutrients and neighbors in root foraging processes. Methodology/Principal Findings The experiment was conducted in split-containers, wherein half of the roots of spruce (Picea asperata) seedlings were subjected to intraspecific root competition (the vegetated half), while the other half experienced no competition (the non-vegetated half). Experimental treatments included fertilization in the vegetated half (FV), the non-vegetated half (FNV), and both compartments (F), as well as no fertilization (NF). The root architecture indicators consisted of the number of root tips over the root surface (RTRS), the length percentage of diameter-based fine root subclasses to total fine root (SRLP), and the length percentage of each root order to total fine root (ROLP). The target plants used novel root foraging behaviors under different combinations of neighboring plant and localized fertilization. In addition, the significant increase in the RTRS of 0–0.2 mm fine roots after fertilization of the vegetated half alone and its significant decrease in fertilizer was applied throughout the plant clearly showed that plant root foraging behavior was regulated by local responses coupled with systemic control mechanisms. Conclusions/Significance We measured the root foraging ability for woody plants by means of root architecture indicators constructed by the roots possessing essential nutrient uptake ability (i.e., the first three root orders), and provided new evidence that plants integrate multiple forms of environmental information, such as nutrient status and neighboring competitors, in a non-additive manner during the root foraging process. The interplay between the responses of individual root modules (repetitive root units) to localized environmental signals and the systemic control of these responses may well account for the non-additive features of the root foraging process.

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

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.

Soil respiration and carbon pools across a range of spruce stand ages, Eastern Tibetan Plateau

Abstract To understand the effects of reforestation on soil carbon (C) dynamics, we measured soil carbon dioxide (CO2) effluxes and soil C pools in dragon spruce (Picea asperata Mast.) stands of various ages (22-, 47- and 68-year-old dragon spruce plantations, and a 150-year-old primeval coniferous forest) in the eastern Tibet Plateau. The soil respiration rate of all the stands increased from March, followed by a peak in late July to August with temporal fluctuations, and then dramatically declined in September. The annual total soil CO2 effluxes (Rtot), soil heterotrophic CO2 effluxes (Rh), and soil autotrophic CO2 effluxes (Ra) were higher in the 22- (1004, 656 and 348 g C m−2 year−1, respectively) and 150-year-old stands (1070, 712 and 358 g C m−2 year−1, respectively), and lower in the 47- (792, 543 and 249 g C m−2 year−1, respectively) and 68-year-old stands (952, 607 and 345 g C m−2 year−1, respectively). The soil total organic carbon (TOC), easily oxidizable organic C (EOC), microbial biomass C (MBC), and particulate organic C (POC) pools at depths ranging from 0 cm to 30 cm decreased within 68 years after tree planting. The TOC and its different components in the 0 cm to 10 cm soil layer were significantly and positively related with Rh and Rtot (p < 0.01). The TOC contents (0 cm to 10 cm soil layer) in the primary forest (77.6 g kg−1) were about 1.87, 2.51 and 3.14 times higher than those in the 22-, 47- and 68-year-old plantations, respectively. Our results indicated soil respiration and soil C contents firstly decreased but then increased with stand age, and 68 years of reforestation has caused substantial depletion of soil CO2 effluxes and carbon pools.

Responses of nutrient capture and fine root morphology of subalpine coniferous tree Picea asperata to nutrient heterogeneity and competition

Investigating the responses of trees to the heterogeneous distribution of nutrients in soil and simultaneous presence of neighboring roots could strengthen the understanding of an influential mechanism on tree growth and provide a scientific basis for forest management. Here, we conducted two split-pot experiments to investigate the effects of nutrient heterogeneity and intraspecific competition on the fine root morphology and nutrient capture of Picea asperata. The results showed that P. asperata efficiently captured nutrients by increasing the specific root length (SRL) and specific root area (SRA) of first-and second-order roots and decreasing the tissue density of first-order roots to avoid competition for resources and space with neighboring roots. The nutrient heterogeneity and addition of fertilization did not affect the fine root morphology, but enhanced the P and K concentrations in the fine roots in the absence of a competitor. On the interaction between nutrient heterogeneity and competition, competition decreased the SRL and SRA but enhanced the capture of K under heterogeneous soil compared with under homogeneous soil. Additionally, the P concentration, but not the K concentration, was linearly correlated to root morphology in heterogeneous soil, even when competition was present. The results suggested that root morphological features were only stimulated when the soil nutrients were insufficient for plant growth and the nutrients accumulations by root were mainly affected by the soil nutrients more than the root morphology.