Mount Gongga Research Articles

Effects of transport on aerosols over the eastern slope of the Tibetan Plateau: synergistic contribution of Southeast Asia and the Sichuan Basin

The aerosol optical properties and chemical components of PM2.1 (particulate matter with a diameter of 2.1 µm or less) were investigated at Mount Gongga on the eastern slope of the Tibetan Plateau ...

Spatial‐Temporal Patterns of Evapotranspiration Along an Elevation Gradient on Mount Gongga, Southwest China

AbstractEvapotranspiration (ET) is a crucial component of the hydrological cycle in terrestrial ecosystems, but estimating ET in mountainous regions is challenging. In this study, the performance of a generalized nonlinear formulation of the complementary principle while estimating daily ET was evaluated, and the spatial‐temporal variation of ET was analyzed across four vegetation types along an elevation gradient on Mount Gongga, Southwest China. The values of the calibrated Priestley and Taylor coefficients for each of the four sites ranged from 0.98 to 1.13. The correlation coefficients between the estimated and observed daily actual evapotranspiration for each of the four sites ranged from 0.71 to 0.92. A markedly asymmetrical complementary relationship existed among the four studied sites, and the values showed less scattered during the wet season. The annual ET rates were 779.12, 781.63, 701.77, and 625.17 mm/yr in the broadleaf forest (BLF), broadleaf and coniferous mixed forest (BCF), coniferous forest (CF), and shrub land (SL), respectively, and showed a decreasing trend of 9.72 mm per 100 m along the elevation gradient. After recalibration of the seasonal αe values, the estimated annual ET rates increased and were closer to the observed values in BLF and BCF. The results indicate that daily ET in mountainous areas can be estimated using the generalized nonlinear formulation of the complementary relationship together with routine meteorological data alone, but seasonal changes in αe values should be taken into consideration in forests with deciduous trees.

Quantitative Western-blot profiles of factor H and factor H-related proteins in atypical haemolytic uraemic syndrome and C3 glomerulopathy

Conifers are the largest and ecologically and economically most important component group of the gymnosperms. Despite their slow rate of molecular evolution, rapid and recent diversification was unexpectedly prevalent in this ancient group in the Hengduan Mountains, a world’s biodiversity hotspot and gymnosperm diversity center in Southwest China. In this study, we investigated the underlying mechanisms and disentangled the interactions of geography and ecology in speciation and evolution in Pinus armandii, an important forest tree species endemic to China, by integrating analyses of population transcriptomics, population genetics and ecological niche modeling. Many lines of evidence suggest that cryptic speciation has occurred in P. armandii. During the process, geologically induced formation of Mount Gongga and other massive peaks might trigger the initial vicariance isolation of the northern and southern subdivisions, and ecologically based selection then reinforced their differentiation and local adaptation. Our ecological niche analysis and earlier reciprocal transplant experiments in P. armandii provided convincing evidences for the critical role of ecology in the process of speciation. These findings suggest that both geography and ecology contributed significantly to the abundance of very recent and rapid species divergences, which promoted the rising of the extremely high conifer diversity in the Hengduan Mountains.

Bioaccumulation of Heavy Metals in Twigs and Leaves of Abies fabri at Mount Gongga in China: A Comparison Study Between 1999 and 2014

The rapid economy growth led to the environmental carrying capacity reaching the maximum level.Given that the time changing trend of heavy metal pollution in the remote forest ecosystems has rarely been reported, we reported the differences of Pb, Hg, Cd, As, Cr, Mn, Cu, Zn and bioaccumulation in twigs and leaves of fir(Abies fabri) between samples collected in 1999 and 2014 at the Mt. Gongga, which was located at eastern Tibet Plateau. Our results suggested that the concentrations of Pb, Hg, As, Cd, Mn and Cu in the samples collected in 1999 were significantly higher than those collected in 2014, while the concentrations of Cr, Zn and Ba in samples collected in 2014 were higher than those collected in 1999. The correlation analysis indicated that concentrations of Pb, Hg, Cr, As, Cd, Mn, Cu, Zn and Ba in leaves were positive correlated to the age of the leaves. In addition, Hg was apt to enrich in leaves while the other metals were prone to enrich in twigs. According to the multiple linear regression result, about 70.6% of Hg in leaves and twigs was from air, while the other heavy metals, including Pb, Cr, As, Cd, Cu, Zn, and Ba, were mainly from soil(42.3%-92.2%). These results suggest that there may be different accumulation mechanisms in forest ecosystems between Hg and the other heavy metals.

Altitudinal effect of soil n-alkane δD values on the eastern Tibetan Plateau and their increasing isotopic fractionation with altitude

Stable isotope paleoaltimetry has provided unprecedented insights into the topographic histories of many of the world’s highest mountain ranges. However, on the Tibetan Plateau (TP), stable isotopes from paleosols generally yield much higher paleoaltitudes than those based on fossils. It is therefore essential when attempting to interpret accurately this region’s paleoaltitudes that the empirical calibrations of local stable isotopes and the relations between them are established. Additionally, it is vital that careful estimations be made when estimate how different isotopes sourced from different areas may have been influenced by different controls. We present here 29 hydrogen isotopic values for leaf wax-derived n -alkanes (i.e., δ Dwax values, and abundance-weighted average δ D values of C29 and C31) in surface soils, as well as the δ D values of soil water ( δ Dsw) samples (totaling 22) from Mount Longmen (LM), on the eastern TP (altitude ~0.8–4.0 km above sea level (asl), a region climatically affected by the East Asian Monsoon (EAM). We compared our results with published data from Mount Gongga (GG). In addition, 47 river water samples, 55 spring water samples, and the daily and monthly summer precipitation records (from May to October, 2015) from two precipitation observation stations were collected along the GG transect for δ D analysis. LM soil δ Dwax values showed regional differences and responded strongly to altitude, varying from ‒160‰ to ‒219‰, with an altitudinal lapse rate (ALR) of ‒18 ‰ km‒1 ( R 2=0.83; p n =29). These δ Dwax values appeared more enriched than those from the GG transect by ~40‰. We found that both the climate and moisture sources led to the differences observed in soil δ Dwax values between the LM and GG transects. We found that, as a general rule, e wax/rw, e wax/p and e wax/sw values (i.e., the isotopic fractionation of δ Dwax corresponding to δ Drw, δ Dp and δ Dsw) increased with increasing altitude along both the LM and GG transects (up to 34‰and 50‰, respectively). Basing its research on a comparative study of δ Dwax, δ Dp, δ Drw( δ Dspringw) and δ Dsw, this paper discusses the effects of moisture recycling, glacier-fed meltwater, relative humidity ( RH ), evapotranspiration ( ET ), vegetation cover, latitude, topography and/or other factors on e wax/p values. Clearly, if e wax-p values at higher altitudes are calculated using smaller e wax-p values from lower altitudes, the calculated paleowater δ Dp values are going to be more depleted than the actual δ D values, and any paleoaltitude would therefore be overestimated.

Patterns and drivers of fungal diversity along an altitudinal gradient on Mount Gongga, China

Fungi are essential components of soil microbial communities and have a crucial role in biogeochemical processes. Alpine regions are sensitive to climate change, and the importance of changes in fungal community composition along altitudinal gradients in alpine regions is hotly debated. We used 454 pyrosequencing approaches to investigate the fungal communities at 1600, 2300, 2800, 3000, and 3900 m above sea level along an altitudinal gradient on Mount Gongga. The results showed that Agaricomycetes, Sordariomycetes, and Tremellomycetes are the dominant classes at all sampling sites. Operational taxonomic unit richness decreased with increasing altitude, and the fungal communities were clustered into three groups that corresponded to altitudes of, i.e., 1600, 2300, and above 2800 m. The evenness of fungi was not significantly correlated with altitude, whereas beta diversities were significantly correlated with altitude. The distance-based redundancy analysis and Mantel test indicated that the composition of fungal assemblages was mostly driven by altitude and temperature. Our results indicated that ecological processes possibly related to altitude and temperature play an important role in structuring fungal biodiversity along the elevational gradient. Our results highlight that different microbes may respond differently to environmental gradients.

A Negative Relationship between Foliar Carbon Isotope Composition and Mass-Based Nitrogen Concentration on the Eastern Slope of Mount Gongga, China.

Plants adopt ecological strategy to resist environmental changes and increase their resource-use efficiency. The ecological strategy includes changes in physiological traits and leaf morphology, which may result in simultaneous variations in foliar N concentration and the ratio of intercellular CO2 concentration to ambient CO2 concentration (ci/ca). This in turn links to foliar carbon isotope discrimination, and thus, a relationship between foliar N concentration and foliar carbon isotope composition (δ13C) is expected. To understand how plants integrate their structural and physiological resistance to environmental changes, the relationship between foliar N concentration and foliarδ13C has been assessed intensively, especially the correlation between area-based N concentration (Narea) and δ13C.Less effort has been dedicated to the examination of the relationship between mass-based N concentration(Nmass) and δ13C. Studies on the Nmass–δ13C relationship, especially those including a large amount of data and species, will enhance our understanding of leaf economics and benefit ecological modeling. The present study includes an intensive investigation into this relationship by measuring foliar Nmass and δ13C in a large number of plant species grown on the eastern slope of Mount Gongga, China. This study shows that foliar Nmass decreases with increasing δ13C, which is independent of functional group, vegetation type, and altitude. This suggests that a negative correlation between Nmass and δ13C may be a general pattern for plants grown not only on Mount Gongga, but also in other areas.

Decoupling of nutrient element cycles in soil and plants across an altitude gradient.

Previous studies have examined the decoupling of C, N, and P under rapid changes in climate. While this may occur in different environment types, such climactic changes have been reported over short distances in mountainous terrain. We hypothesized that the decoupling of C, N, and P could also occur in response to increases in altitude. We sampled soil and plants from Mount Gongga, Sichuan Province, China. Soil C and N were not related to altitude, whereas soil P increased with altitude. Soil N did not change with mean annual temperature (MAT), mean annual precipitation (MAP), vegetation and soil types, whereas soil P varied with MAT and vegetation type. Plant C remained constant with increasing altitude; plant N exhibited a quadratic change trend along the altitude gradient, with a turning point at 2350 m above average sea level; and plant P decreased with altitude. MAP mostly accounted for the variation in plant P. MAT was responsible for the variation of plant N at elevations below 2350 m, whereas MAT and vegetation type were the dominant influential factors of plants growing above 2350 m. Thus, the decoupling of C, N, and P in both soil and plants was significantly affected by altitude.

Heterogeneity in supraglacial debris thickness and its role in glacier mass changes of the Mount Gongga

In the Tibetan Plateau, many glaciers have extensive covers of supraglacial debris in their ablation zones, which affects glacier response to climate change by altering ice melting and spatial patterns of mass loss. Insufficient debris thickness data make it difficult to analyze regional debris-cover effects. Maritime glaciers of the Mount Gongga have been characterized by a substantial reduction in glacier area and ice mass in recent decades. The thermal property of the debris layer estimated from remotely sensed data reveals that debris-covered glaciers are dominant in this region, on which the proportion of debris cover to total glacier area varies from 1.74% to 53.0%. Using a physically-based debris-cover effect assessment model, we found that although the presence of supraglacial debris has a significant insulating effect on heavily debris-covered glaciers, it accelerates ice melting on ~10.2% of total ablation zone and produces rapid wastage of ~25% of the debris-covered glaciers, leading to the similar mass losses between the debris-covered and debris-free glaciers. Widespread debris cover also facilitates the development of active terminus regions. Regional differences in debris-cover effects are apparent, highlighting the importance of debris cover for understanding glacier mass changes in the Tibetan Plateau and other mountain ranges around the world.

Gaultheria gonggashanensis sp. nov. (Ericaceae) from Sichuan, China

Gaultheria gonggashanensis P. W. Fritsch & Lu Lu, a new species from western Sichuan Province, China, is described and illustrated. This species belongs to Gaultheria ser. Trichophyllae Airy Shaw and is most similar to G. sinensis J. Anthony, but differs by its longer stem setae, glabrous petioles and leaf blade midveins adaxially, thick‐chartaceous to subcoriaceous leaf blades, larger calyx lobes, and smaller anther thecae. The species is known with certainty only from the Hailuo Valley on the east slope of Mount Gongga in the Daxue Range.

Tracing the Sources and Processes of Groundwater in an Alpine Glacierized Region in Southwest China: Evidence from Environmental Isotopes

The melting of alpine snow and glaciers is an important hydrologic process on Mount Gongga, China. The relevance of ice-snow melt to the groundwater recharge in the glacierized Hailuogou watershed is so far not well known. To better understand the origin of groundwater and the hydrological interactions between groundwater, meltwater, and precipitation in this region, 148 environmental isotopic data of water samples were analyzed for changes in isotopic composition. The results indicate that the groundwater contains a uniform isotopic signature, with δ18O values between −13.5‰ and −11.1‰ and δ2H values between −90‰ and −75‰. The mean stable isotopic composition of groundwater is heavier than that of ice-snow meltwater but lighter than that of precipitation. The effect of evaporation on the isotopic variation of groundwater is very limited and the seasonal isotope variations in precipitation are attenuated in groundwater. A model based on the δ18O results suggests that approximately 35% of the groundwater is derived from ice-snow meltwater sources. The study demonstrates that ice-snow meltwater is a substantial source of shallow groundwater in the alpine regions on the edge of the Tibetan Plateau.

DNA barcoding and regional diversity of understudied Micropeplinae (Coleoptera: Staphylinidae) in Southwest China: phylogenetic implications and a new Micropeplus from Mount Emei.

Extensive litter sampling at eight forested localities in Yunnan and Sichuan detected 381 specimens of Micropeplinae rove beetles. DNA barcoding data from 85 representative specimens were analysed to delimit species and infer their relationships. Statistical methods were implemented to assess regional species diversity of understudied Micropeplinae. The total number of sampled Micropeplinae species varied between 14 and 17, depending on a splitting versus lumping approach for allopatric populations. A single Micropeplinae species was sampled in six of eight studied localities, three species were found on Mount Gongga, while ten species were discovered on hyperdiverse Mount Emei in Sichuan. All Micropeplinae specimens from our samples belong either to the genus Cerapeplus, or to three other inclusive groups temporarily retained inside Micropeplus sensu lato. Each of the three groups potentially represents a separate genus: tesserula group, sculptus group and Micropeplus sensu stricto. A new species Micropeplus jason sp. n. from Mount Emei in Sichuan is described. Numerous illustrations introduce regional fauna and clarify the discussed morphological characters.

Recent Climate Changes in Hailuogou Watershed on the Eastern Slope of Mount Gongga, South-Eastern Fringe of the Tibetan Plateau, China

Mountainous regions are particularly sensitive to climate change. Seasonal and annual variations in climate already strongly influence the ecosystems in such areas. Temporal and spatial variations of temperature and precipitation, for higher elevation site (Hailuogou Station) and lower elevation site (Moxi Station) within Hailuogou watershed which is located on the eastern slope of Mount Gongga, China, were analyzed to evaluate the extent and trend of climate change. Climate data were carefully checked and corrected for errors before being analyzed. The results of this work indicate that the measured climate data contain a wide magnitude of variations in temperature and precipitation in the mountainous region. The annual, minimal and maximal temperatures exhibit some increasing trends during the studied period. The results of this work show that slightly warming climate is mostly caused by increasing minimum temperature. Maximal precipitation mostly occurs in July and minimal precipitation mostly occurs in December. There exists a slightly declining trend of precipitation during 1988-2009. Precipitation exhibits an increasing trend with altitude, whereas the temperature has the reverse trend in the alpine area during studied period.

A comparative study on stable isotopic composition in waters of the glacial and nonglacial rivers in Mount Gongga, China

AbstractHailuogou (HLG) River and Huangbengliu (HBL) Gulley are typical alpine glacial and nonglacial rivers in Mount Gongga China, respectively. To differentiate distinct hydrologic regimes of the two rivers, δ18O and δ2H were measured on 196 water samples collected almost monthly from May 2008 to December 2009. The results indicate that: (i) the measured isotopic data show that stream water is overall isotopically more enriched in 2H and 18O than ice‐snow meltwater but more depleted than precipitation and ground water; (ii) these data also suggest that stream flow is generally more dominated by ice‐snow meltwater in HLG River than in HBL Gulley; (iii) δ2H/δ18O relationship suggests that isotopic composition of precipitation is well preserved in stream flow, and evaporation is only minor in both HBL Gulley and HLG River; (iv) this study highlights that ice‐snow meltwater is a substantially important water source in alpine regions on south‐eastern edge of Tibetan Plateau.

Rainfall Interception in Two Contrasting Forest Types in the Mount Gongga Area of Eastern Tibet, China

An important component of the water cycle in ecological systems, rainfall interception by virgin forests was here calculated from gross precipitation minus through fall and stem flow. The through fall measurement system was designed on the basis of a 3 m long trough mounted beneath the canopy and able to operate successfully under a range of rainfall conditions. Stem flow was measured using spiral collars consisting of a split plastic hose attached to sampled trees, with gross precipitation measured in an open area via a tipping-bucket rain gauge. This study was carried out to evaluate rainfall interception and distribution patterns of gross precipitation in two contrasting rainforest types (coniferous and broadleaved/coniferous mixed) in the Mount Gongga area on the eastern fringe of Tibet, China, from 2008 to 2009. Net precipitation was found to be primarily composed of through fall, while stem flow contributed less than 0.5% (0.1% and 0.4% in conifer and mixed forest, respectively) to total gross precipitation (GP) and was thus negligible in both forest types. The difference in the interception loss fraction between conifer and mixed forest was greater than 30%, with the interception loss of the former apparently more than that of the latter mainly due to the increased presence of small droplets produced by coniferous leaves. Additionally, interception loss in conifer forest was more dependent on rainfall than that in mixed forest. In contrast, through fall and stem flow exhibited the opposite pattern, likely attributable to a through fall lag of 8 to 10 h after rainfall in mixed forest but not in conifer forest.

Altitudinal Variation in Leaf Nitrogen Concentration on the Eastern Slope of Mount Gongga on the Tibetan Plateau, China

Mount Gongga spans 6500 m in elevation and has intact and continuous vertical vegetation belts, ranging from subtropical evergreen broad-leaved vegetation to an alpine frigid sparse grass and desert zone. Investigating the altitudinal trends in leaf nitrogen (N) on Mount Gongga can increase our understanding of the global biogeography of foliar N. In this study, 460 leaf samples from mosses, ferns, and seed plants were collected along an altitudinal gradient on the eastern slope of Mount Gongga, and the variation in leaf N concentration (mass basis) with elevation was analyzed. There are considerable differences in leaf N between mosses and ferns, mosses and seed plants, C4 and C3 plants, and evergreen and deciduous woody plants. The general altitudial pattern of leaf N in Mount Gongga plants was that leaf N kept increasing until an elevation of about 2200 m above sea level, with a corresponding mean annual temperature (MAT) of 8.5°C, and then decreased with increasing elevation. However, the evergreen woody plants displayed a decline trend in leaf N across the altitude gradient. Our findings provide an insight into the altitudinal variation in leaf N.

Stable isotopic information for hydrological investigation in Hailuogou watershed on the eastern slope of Mount Gongga, China

Hydrological systems have been seriously affected by changes of glaciations and snow covers in Mount Gongga, Sichuan, China, but the relevance of ice-snow melt for alpine river basin hydrology is so far not well known. To better understand hydrological features of the Hailuogou River, changes of δ18O and δ2H were investigated by analyzing 117 water samples collected from May 2008 to November 2009. Our results show that the stream water contains a relatively intermediate magnitude of isotopic variations, with δ18O ranging from −18.09 to −13.08 ‰ and δ2H from −126.5 to −88.8 ‰. The average values are both higher than those of ice-snow meltwater, but lower than those of meteoric water. These data also show a gradually increasing trend from upstream to downstream, and these changes might document the fingerprint of ice-snow melt in the headwater region and indicate the increasing recharge of heavy isotope-enriched waters with flow distance. The similarity in slopes of δ2H and δ18O relationship for meteoric waters and stream waters suggests that the isotopic signature of precipitation is well preserved in stream flow, and during the rainfall and stream flow the evaporation is only minor. Based on δ18O model, the results suggested that the fraction of ice-snow meltwater input over the total stream flow ranged from 84.50 to 86.52 % in the headwater region, but the fraction of ice-snow meltwater input from upper basin downward was significantly decreased. The study demonstrates that ice-snow meltwater is a substantially important water source in alpine regions on the edge of Tibetan Plateau.

Comparison of element concentrations in fir and rhododendron leaves and twigs along an altitudinal gradient

Concentrations of 23 elements (Ca, K, Mg, P, Al, Cu, Fe, Mn, Mo, Na, Ni, Zn, Ag, Ba, Be, Cd, Co, Cr, Pb, Sb, Th, Tl, and V) in leaf and twig samples of a fir (Abies fabri) and a rhododendron (Rhododendron williamsianum) collected along an altitudinal gradient on Mount Gongga, China, are reported in the present study. Most of the macronutrients (K and P), micronutrients (Fe, Zn, Cu, Na, Ni, Mo, and Al), and trace elements (Pb, Tl, Ag, Cd, Ba, Co, V, Be, and Cr) are significantly enriched in fir when compared to rhododendron; however, Ca, Mg, Mn, Ba, and Cd are more enriched in rhododendron than in fir. Most of the elements in both plants are more significantly enriched in twigs than in leaves. The relationship between element concentration in plants and altitudinal gradient is nonlinear. Altitudes of 3,200 and 3,400 m are turning points for fir and rhododendron growth, respectively. Concentrations of all trace elements in the two plants along the altitudinal gradient are well below the toxic level in plants. No known industrial sources of the elements investigated exist in the Mount Gongga area, China. Element concentrations in the present study are higher than those found in mosses collected from the same area, indicating that the area is not contaminated. The element concentrations that we observed in plant samples were due to soil uptake. The pronounced differences between the two species are due to the different uptake characteristics of fir and rhododendron.

Distribution of debris thickness and its effect on ice melt at Hailuogou glacier, southeastern Tibetan Plateau, using in situ surveys and ASTER imagery

AbstractDebris cover is widely present in glacier ablation areas of the Tibetan Plateau, and its spatial distribution greatly affects glacier melt rates. High-resolution in situ measurements of debris thickness on Hailuogou glacier, Mount Gongga, southeastern Tibetan Plateau, show pronounced inhomogeneous debris distribution. An analysis of transverse and longitudinal profiles indicates that the ground-surveyed debris thicknesses and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)-derived thermal resistances of debris layers correlate strongly over the entire ablation area. Across- and along-glacier patterns of ASTER-derived thermal resistance correspond well with spatial patterns of debris thickness, which may reflect large-scale variations in the extent and thickness of the debris cover. The ice melt rate variability over the ablation area simulated by a surface energy-balance model that considered thermal resistance of the debris layer indicates clearly the crucial role of debris and its spatial continuity in modifying the spatial characteristics of melt rates. Because of the inhomogeneous distribution of debris thickness, about 67% of the ablation area on Hailuogou glacier has undergone accelerated melting, whereas about 19% of the ablation area has experienced inhibited melting, and the sub-debris melt rate equals the bare-ice melt rate in only 14% of the ablation area.

Measurements of nitrogen isotope composition of plants and surface soils along the altitudinal transect of the eastern slope of Mount Gongga in southwest China

The natural abundances of stable nitrogen isotopes in plants and soils have been viewed as recorders that can be used to reconstruct paleoclimate and ecological processes or to indicate the biogeochemical cycle of nitrogen in nature. This study systematically measured the nitrogen isotope composition (δ(15)N) in plants and surface soils along an altitudinal transect of elevation range of 1200 to 4500 m on the eastern slope of Mount Gongga in southwest China. The influences of photosynthetic pathways on plant δ(15)N as well as the effects of temperature and precipitation on δ(15)N altitudinal trends in plants and surface soils are discussed. Across this altitude transect, the δ(15)N values of C(3) and C(4) plants on Mount Gongga range between -9.87‰ and 7.58‰ with a mean value of -1.33‰, and between -3.98‰ and 4.38‰ with a mean value of -0.25‰, respectively. There is an evident δ(15)N difference between C(3) plants and C(4) plants. If, however, you only compare C(4) plants with those C(3) plants growing at the same altitudinal range, no significant difference in δ(15)N exists between them, suggesting that photosynthetic pathway does not have an influence on the plant δ(15)N values. In addition, we found that C(3), C(4) plants and surface soil (0-5 cm depth) all trend significantly towards more negative δ(15)N with increasing elevation. Furthermore, this study shows that the mean annual temperature and the mean annual precipitation positively and negatively correlate with δ(15)N in C(3) and C(4) plants, respectively. This indicates that precipitation and temperature are the main controlling factors of the δ(15)N variation in plants with altitude. We propose that lower δ(15)N values of plants and soils at higher altitude should be attributed to lower mineralization and lower net nitrification rates induced by low temperature and abundant rainfall.