Elsevier

CATENA

Volume 142, July 2016, Pages 102-111
CATENA

Variations in soil phosphorus biogeochemistry across six vegetation types along an altitudinal gradient in SW China

https://doi.org/10.1016/j.catena.2016.03.004Get rights and content

Highlights

  • Soil P biogeochemistry across 7 altitudes with 6 vegetation types was studied.

  • The TP stock was higher in 3838–4235 m than that in 2032–3614 m.

  • Labile P showed a parabolic trend with an altitude that was inverse with HCl-Pi.

  • Variation of labile P along the gradient was mainly impacted by soil pH and vegetation type.

  • Temperature is an additional factor affecting change of labile P in 3060–4235 m.

Abstract

The impacts and relative importance of temperature, precipitation, lithology, soil properties, vegetation type and microbial activity on soil P biogeochemistry along altitudinal gradients are poorly understood. Our aim is to reveal the variations and main driving factors governing soil P forms across six different vegetation types along an altitudinal gradient (2032–4235 m asl) on Mt. Gongga, southwest China. Soil P forms were measured using a sequential fractionation technique. The results showed that the spatial distributions of total P and organic P clearly exhibited altitudinal variations along the gradient. The total P stocks in the 3838–4235 m zones were significantly higher than those in the 2032–3614 m zones. This pattern is likely influenced by climate, soil erosion, total P content in the parent material and vegetation type. Unlike the total P stock, the concentrations and stocks of available P in the surface soils showed a parabolic pattern with altitude, with maximums at the 3060 m site and minimums at the lowest site. The Ca-Pi concentrations (extracted by 1 M HCl solutions) displayed a spatial pattern opposite to that of the available P. The NaOH-Pi concentrations changed little with altitude and accounted for a small part of the total P. The Ca-Pi represented the largest part of the total P at the 2032 m site and in the alpine zones, whereas the organic P contributed the largest portion of total P in the sub-alpine zones. A redundancy analysis showed that the general spatial pattern of all the P forms was mainly related to soil pH, vegetation and soil organic matter. In particular, the soil pH, which was mainly controlled by vegetation type and precipitation, significantly influenced the altitudinal pattern of Ca-Pi. The effect of soil pH, perhaps coupled with the amount of P returned by litter production, is a crucial factor in the parabolic pattern of available P between 2032 and 4235 m asl. Furthermore, in the 3060–4235 m zone, temperature becomes an additional important factor governing the pattern of available P due to its influence on litter decomposition rates. These results emphasize the central role of vegetation in regulating soil P biogeochemistry along the altitudinal gradient by affecting soil properties and litter production.

Introduction

The understanding of soil phosphorus (P) processes is essential for maintaining sustainable development of mountain ecosystems (Wu et al., 2013a). While most studies on P regimes along altitudinal gradients consider the impact of P on vegetation, the opposite direction (e.g., influences of vegetation on soil P) is poorly understood (Lucas-Borja et al., 2012, Ushio et al., 2010). Soil P bioavailability in natural ecosystems is often simultaneously impacted by lithology (Mage and Porder, 2013), climate (Vincent et al., 2014), soil age (Zhou et al., 2013a), soil properties (Turner and Blackwell, 2013), and biological activity (Richardson et al., 2011). However, most previous studies have focused mainly on one single factor impacting P bioavailability. For example, chronosequences and climosequences have often been used to discuss the influences of soil age (Walker and Syers, 1976) and rainfall (Miller et al., 2001) on biogeochemical P cycling, respectively. Recently, some researchers have noted the need to investigate the interactions (Porder and Chadwick, 2009) and determine the relative importance (Mage and Porder, 2013) of these factors in order to understand P cycling in terrestrial ecosystems. Furthermore, to predict the P status of ecosystems regionally or even globally and to adequately represent P bioavailability in global biogeochemistry-climate models, the relative importance of the impact factors and their synergistic effects on P biogeochemistry should be explored comprehensively (Yang et al., 2013). The vertical vegetation and soil zones on high mountains provide an opportunity for determining the relative importance of the influences of lithology, climate, soil properties, vegetation, and their interactions on the biogeochemical P cycles in natural ecosystems.

There are two important theories that are suitable for explaining variations in soil P bioavailability along altitudinal gradients with similar bedrocks. The first theory is that the soil P bioavailability will decrease with increasing elevation because the decomposition rates of organic P will be reduced due to the decrease in temperature. For example, Vitousek et al. (1988) reported a decreasing trend in available P concentration with increasing elevation in a Hawaiian montane rainforest (760–1585 m asl). In a tropical montane forest in Ecuador, Soethe et al. (2008) also observed that the P availability in the organic horizon decreased with increasing elevation (1900–3000 m asl). Moreover, Vincent et al. (2014) found that the available P concentration decreased upslope in a subarctic tundra landscape (500–1000 m asl).

The second theory is the conceptual model of P evolution with pedogenesis proposed by Walker and Syers (1976). According to this model, the soil P bioavailability will decrease with increasing weathering intensity (and thus soil development) because large amounts of available P can be transformed into occluded P and organic P in more developed soils. Therefore, the available P in soils is speculated to decrease downslope as a result of increasing weathering intensity due to the increasing temperature and more developed vegetation.

Mt. Gongga in southwestern China provides an ideal place for examining P biogeochemical cycles across different climates and vegetation types. On the eastern slope of Mt. Gongga, there is an altitudinal difference of 6600 m and, thus, a large temperature and precipitation gradient (Zhong et al., 1999). Seven vegetation zones are distributed between the alpine frigid meadow to the evergreen broad-leaved forest on the slope (Liu and Qiu, 1986). The soil P bioavailability on Mt. Gongga will decrease with altitude according to the first theory but increase with altitude according to the second one. If the effects of vegetation types are considered, the spatial pattern of the P bioavailability along this slope is likely more difficult to predict. For example, a recent study suggested that changes in temperature significantly influenced PO43 –P concentrations in a subarctic region, but the effects of temperature depended strongly on the dominant vegetation type (Sundqvist et al., 2014).

Here, in combination with the relevant geochemical and biological factors, the forms and stocks of soil P were investigated using a modified Hedley fractionation technique (Tiessen and Moir, 1993) on Mt. Gongga. In particular, the aims of the study are the following:

  • (1)

    Revealing the spatial distribution of the soil P bioavailability and forms along the altitudinal zones on Mt. Gongga.

  • (2)

    Because the variations in soil P biogeochemistry along the altitudinal slope are likely influenced by temperature, precipitation, soil properties, vegetation type and microbial activities, the second goal is to identify the main driving factors among these potential factors.

Section snippets

Study area

Mt. Gongga is located in southwestern China at the southeastern edge of the Tibetan Plateau and has an elevation of 7556 m (Fig. S1). The area within 29 km of Mt. Gongga has a total topographic relief of 6600 m because it is located in the transition zone between the Tibetan Plateau and the Sichuan Basin. Due to this huge altitudinal difference and its distance from cities, there are seven pristine altitudinal vegetation zones on the eastern slope of Mt. Gongga (Fig. 1). The climate of the eastern

Physical and chemical soil properties

The mineral compositions of the parent materials were similar and were dominated by granites at all the sites along the slope. The average contributions of feldspar, quartz, hornblende, chlorite, and muscovite were 43.7%, 32.7%, 17.9%, 4.9% and 0.8%, respectively (Fig. S3).

The degree of soil development on the eastern slope of Mt. Gongga increased with decreasing elevation based on the characteristics of the soil profiles (Table 1). The thickness of the A horizons increased downslope. The

Altitudinal pattern of TP

The spatial distribution of TP concentrations shows an altitudinal pattern: the concentrations and stocks of TP in the alpine sites were higher than those in the sub-alpine and the low altitude sites (Fig. 2a, b). This altitudinal pattern of TP is likely a result of the interaction of climate, vegetation type and P contents in the parent materials. First, in the alpine zones, the P in the primary minerals is less depleted due to weaker weathering resulting from the lower temperatures, higher pH

Conclusions

The variations and driving factors of soil P biogeochemistry across six different vegetation types along an altitudinal gradient on Mt. Gongga were investigated. The concentrations and stocks of soil total P in the alpine zones were higher than those in the sub-alpine and low altitude zones. This pattern is likely related to climate, P content in the parent materials, vegetation type and soil erosion. The concentrations and stocks of available P showed a parabolic pattern along the slope, which

Acknowledgments

The authors thank three anonymous reviewers for their constructive comments and suggestions that are helpful in improving the quality of this manuscript. This study was supported by the National Natural Science Foundation of China (Grant No. 41401253 and No. 41272200) and the Chinese Academy of Sciences (Grant No. KZZD-EW-TZ-06).

References (51)

  • T.W. Walker et al.

    The fate of phosphorus during pedogenesis

    Geoderma

    (1976)
  • J. Zhou et al.

    Rapid weathering processes of a 120-year-old chronosequence in the Hailuogou Glacier foreland, Mt. Gongga, SW China

    Geoderma

    (2016)
  • J. Zhou et al.

    Changes of soil phosphorus speciation along a 120-year soil chronosequence in the Hailuogou Glacier retreat area (Gongga Mountain, SW China)

    Geoderma

    (2013)
  • F.H. Chung

    Quantitative interpretation of X-ray diffraction patterns of mixtures. I. Matrix-flushing method for quantitative multicomponent analysis

    J. Appl. Crystallogr.

    (1974)
  • C.C. Cleveland et al.

    C:N:P stoichiometry in soil: is there a “Redfield ratio” for the microbial biomass?

    Biogeochemistry

    (2007)
  • F. Courchesne et al.

    Extractable Al, Fe, Mn, and Si

  • J. Frizano

    Nature, Distribution and Significance of Phosphorus in Forest Soils From Puerto Rico, Chile and Brazil

    (1999)
  • M.J. Hedley et al.

    Changes in inorganic and organic soil-phosphorus fractions induced by cultivation practices and by laboratory incubations

    Soil Sci. Soc. Am. J.

    (1982)
  • E.G. Jobbágy et al.

    The uplift of soil nutrients by plants: biogeochemical consequences across scales

    Ecology

    (2004)
  • A.H. Johnson et al.

    Biogeochemical implications of labile phosphorus in forest soils determined by the Hedley fractionation procedure

    Oecologia

    (2003)
  • W. Koerselman et al.

    The vegetation N:P ratio: a new tool to detect the nature of nutrient limitation

    J. Appl. Ecol.

    (1996)
  • Z.G. Liu et al.

    The main vegetation types and their distribution in the Gongga mountainous region

    Acta Phytoecologica Geobotanica Sin.

    (1986)
  • M.E. Lucas-Borja et al.

    Altitude-related factors but not Pinus community exert a dominant role over chemical and microbiological properties of a Mediterranean humid soil

    Eur. J. Soil Sci.

    (2012)
  • J. Luo et al.

    Characteristics of nutrient biocycling of natural forests on the Gongga Mountain

    J. Beijing For. Univ.

    (2005)
  • J. Luo et al.

    A study of the biomass and production of forest on the Gongga Mountain

    Acta Phytoecologica Sin.

    (2000)
  • Cited by (0)

    View full text