SummaryBiomass allocation can exert a great influence on plant resource acquisition and nutrient use. However, the role of biomass allocation strategies in shaping plant community composition under nutrient limitations remains poorly addressed.We hypothesized that species-specific allocation strategies can affect plant adaptation to nutrient limitations, resulting in species turnover and changes in community-level biomass allocations across nutrient gradients. In this study, we measured species abundance and the concentrations of nitrogen and phosphorus in leaves and soil nutrients in an arid-hot grassland. We quantified species-specific allocation parameters for stems vs leaves based on allometric scaling relationships. Species-specific stem vs leaf allocation parameters were weighted with species abundances to calculate the community-weighted means driven by species turnover.We found that the community-weighted means of biomass allocation parameters were significantly related to the soil nutrient gradient as well as to leaf stoichiometry, indicating that species-specific allocation strategies can affect plant adaptation to nutrient limitations in the studied grassland. Species that allocate less to stems than leaves tend to dominate nutrientlimited environments.The results support the hypothesis that species-specific allocations affect plant adaptation to nutrient limitations. The allocation trade-off between stems and leaves has the potential to greatly affect plant distribution across nutrient gradients.
Gully initiation has been a subject of much discussion in the field of gully erosion. Gully initiation could be examined by the S-A relationship (S = aA Àb ) between the critical slope of the gully head (S) and the upstream drainage area (A). Gully erosion plays an important role in sediment yield and land degradation in the Dry-hot Valley region of Southwest China; however, little research has focused on gully development in this region. This study investigated gully morphology and the critical topographic threshold of permanent gullies in Yuanmou Dry-hot Valley. Data for 36 gully heads were derived from the gully digital elevation model created by high-precision real-time kinematic GPS (RTK GPS). A significant relationship between gully length and volume (r 2 = 0.77, p < 0.01) was found to exist, indicating that gully length can be used to estimate the gully erosion rate. Additionally, as vegetation coverage inside the gully increases, the gully morphology tends to be stable. The S-A relationship was S = 0.5195A À0.0899 , while AS 2 values ranged between 4.2 and 758.5 m 2 . The low value of constant b (0.0899) indicates that collapse of the gully wall is the dominant process of gully erosion in Yuanmou Dry-hot Valley.
Vegetation on gully beds could intercept runoff, reduce incision of gully bed, and trap sediment from upstream area. The aim of this study is to evaluate the influences of vegetation buffer strips on concentrated flow hydraulics and gully bed erosion downstream of gully headcuts. Five gully head plots containing different buffer strip widths with similar vegetation density were constructed for in situ scouring experiments. Each plot received 11 tests with 2 discharges (i.e., 7 tests simulating 83.3 L min−1 and 4 tests simulating 166.7 L min−1). Buffer strips clearly decrease flow hydraulics (about 56–70%) and increase flow resistance (1.2 to 1.5 times) according to the selected hydraulic parameters. After 11 tests, total net erosion volume (NEV) and average sediment concentration from each gully bed showed an exponential decreasing relationship with increasing widths of buffer strips. All the selected hydraulic parameters showed a strong correlation with total NEV from the bare soil sections (0.43 < R2 < .61 with significance level reaching .01), whereas the relationship was very weak in the buffer strips. The gross deposition volume in buffer strips showed a linear correlation with upstream NEV (NEVu) and flow velocity (R2 = .91, p < .001). Split flow effects expressed by braid index increased with increasing widths of buffer strips and scouring times. Both bare and vegetated sections suffered from erosion clearly, but the average NEV from buffer strips was about 30.2% of bare soil sections. This indicated the buffer strip effects on reducing erosion were more significant than trapping sediments were in this study.
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