Abstract
Knowledge of altitudinal patterns in soil C, N and P distribution is important for understanding biogeochemical processes in mountainous forests, yet the influence of slope aspects on soil stoichiometry has been largely neglected in previous studies. In this paper, a total number of 150 topsoil samples at four altitudes (3700, 3900, 4100, 4380 m a.s.l.) on sunny and shady slopes of Sygera mountains in the Southeastern Tibet were collected. Soil C, N and P contents, and pH, were measured. Soil temperature, moisture and richness of plant species were investigated at each sampling site. The results showed that: 1) in sunny slope, soil C, N and P concentrations increased with the increase in altitude, whereas soil C:N, C:P, and N:P decreased along the altitudinal gradient on s. Soil moisture was the main regulator of soil nutrition and stoichiometric ratios. 2) In shady slope, soil C and N contents had no significant difference along the altitudinal gradient except the higher values at low altitude, whereas soil P increased first and then decreased. Soil C:N increased with the increase in altitude, whereas C:P and N:P decreased first and then increased. Soil temperature and species richness were the main factors influencing soil nutrition and stoichiometric ratios. 3) Decoupling of soil C:N:P stoichiometry was observed in shady slope owing to changes in soil pH and temperature. 4) The rich contents of soil C and P were observed at two slopes along the altitudinal gradient, and high capacity of N supply existed at the topsoil in shady slope. These results suggested that slope aspect plays an important role in shaping the altitudinal pattern of soil C:N:P stoichiometry in mountainous forests.
Highlights
Stoichiometry of soil carbon (C), nitrogen (N) and phosphorus (P) is important foundation for understanding biogeochemical processes in terrestrial ecosystems
Soil temperature decreased with the increasing altitude, and their values were significantly higher in sunny slope than in shady slope at the same altitude (Fig. 2a)
Species richness decreased with the increase in altitude at both slopes and it was consistently higher in shady slope than sunny slope (Fig. 2d)
Summary
Stoichiometry of soil carbon (C), nitrogen (N) and phosphorus (P) is important foundation for understanding biogeochemical processes in terrestrial ecosystems. There are reports that soil C and N concentrations were higher at medium altitudes than that at low or high altitudes, and P concentrations increased significantly with the rising of altitude, suggesting an increase in N limitation to forests at higher elevations [34]. Other studies observed that soil C and N concentrations were relatively stable along the altitudinal gradients, but soil P concentration kept a decreasing trend with the increase in elevation, suggesting an increase in P limitation to forests at higher elevations [5]. With regard to the ratios of these elements, previous studies showed that, with increase in altitude, soil C:N and C:P initially decrease and increase, whereas N:P is opposite [6], whereas others showed a consistent increase in soil C:N, C:P and N:P with increase in altitude [7]. The altitudinal pattern of C, N, P and their ratios is still inconclusive
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