Assessment of Soil Physicochemical Properties along an Altitude Gradient in High Altitude Region of Gangotri National Park, Uttarakhand, India

The present study was undertaken in the sub-alpine and alpine region of Gangotri valley of Gangotri National Park (GNP) in the Uttarkashi district of Uttarakhand, India. Results showed that selected soils were sandy loam (83%) throughout the region. Soil reactions (pH) vary from 5.00 – 6.28 and showed acidic to the slightly neutral condition. The mean soil Nitrogen (N), and Phosphorus (P) content were calculated 0.37 ± 0.02% and 0.35 ± 0.02%. The value of NP first increased and then decreased along the elevation. Nitrogen and Phosphorus values ranged from 0.01-0.73 and 0.13-0.87. The correlation analysis among the different soil parameters showed that Soil Organic Carbon (SOC) was positively correlated with soil moisture(r = 0.661, p = 0.038); Phosphorus (r = 0.794, p = 0.006) and Nitrogen (r = 0.964, p = 0). SOC and soil moisture increases at the middle elevation (3400-3500 m and 3700-3800 m) and further decreases along the elevation. This may be explained as the impact of long term human influence and altering the natural habitat in the form of a camping spot for trekkers at this elevation and presence of mixed forest (subalpine deodar, pine, and birch) at 3400-3500 m elevational range. This baseline information on soil parameters in Gangotri valley may further help in climate change study in the current scenario of global warming in relation with above ground vegetation and underground soil biota to understand the soil food web dynamics. affected by the soil Nitrogen content (N), Phosphorus (P), and soil pH 1 . Variation in physiochemical properties of forest soil occurs due to variation in climate, soil flora and fauna activities, weathering processes, topography, vegetation cover and other biotic and abiotic variables. In soil formation, vegetation plays a key role as plants litter from aboveground and root detritus below ground are the major source of Soil Organic Matter (SOM) which influences the soil properties such as pH, Soil Organic Carbon (SOC), soil texture 2 . Changes in soil properties can be seen with disturbances.


Introduction
The composition of the forest stand and ground cover is influenced by the forest soil as it is highly affected by the soil Nitrogen content (N), Phosphorus (P), and soil pH 1 . Variation in physiochemical properties of forest soil occurs due to variation in climate, soil flora and fauna activities, weathering processes, topography, vegetation cover and other biotic and abiotic variables. In soil formation, vegetation plays a key role as plants litter from aboveground and root detritus below ground are the major source of Soil Organic Matter (SOM) which influences the soil properties such as pH, Soil Organic Carbon (SOC), soil texture 2 . Changes in soil properties can be seen with disturbances.
Among all nutrient elements availability of soil, Phosphorus is known to affect plant production as more than 80% of the soil Phosphorus gets fixed and become unavailable for plants 4 . In most ecosystems, Nitrogen is considered as a primary limiting micronutrient but in higher altitude alpine and temperate regions availability of Phosphorus may act as a primary limiting element 10 . It has been found that the availability/concentration of Phosphorus in the Indian Himalayan Region (IHR) vegetation is less than the other high altitude forests in the world 17 . Work has been done on soil characteristics and classification in various regions of IHR by many workers 3,5,7,8,11,12 . The literature on soil characterization reveals that data has been documented mainly for the lesser Himalayan region in Himachal Pradesh and Jammu and Kashmir and the other Himalayan States but scanty literature is available for higher altitudinal regions of Uttarakhand. The soil physicochemical properties in high altitude region of the sub-alpine and alpine zone of the Uttarakhand Himalaya are not fully explored. There is a huge void in knowledge about soil physicochemical characteristics along the elevation gradient in high altitudes of the Indian Himalayan region. The present study aimed to assess the physicochemical properties of soil along the elevation gradient in High altitude region of IHR.

Study Area
We selected the Gangotri valley of Gangotri National Park as our study area for soil sample collection ( Figure 1 The area is also rich in faunal diversity and the presence of snow leopard (Panthera uncia), Himalayan brown bear (Ursus arctos isabellinus), wolf (Canis lupus), Musk (Moschus sp.), and blue sheep (Pseudois nayaur) makes it a special ecosystem for biodiversity conservation.

Soil Sampling Procedure
The soil has been sampled along the elevation gradient from different vegetation ranging from 3000-4000 m. At a sampling site, leaf litter (if present) as well as the upper layer of soil was removed. Soil samples were collected at 5-15 cm depth using a soil auger (diameter 3 cm). Elevation was categorized in 100 m class (10 classes) along the altitudinal gradient (3000 m-4000 m). From each class of 100 m elevation, seven composite samples were collected (10 elevation class x 7 composite samples from each class) and 5 subsamples constitute one composite sample. Total of 70 samples were collected along the elevation. These were packed in an airtight polythene bag and transferred to the laboratory of the Wildlife Institute of India for analysis.

Soil Analysis
Different parameters such as soil reaction (pH), soil moisture, organic carbon, and available Nitrogen, Phosphorus and soil texture were analyzed in the laboratory by using standard protocols. A significant variation in soil properties at the different altitudinal range was observed. The processed soil samples were analyzed for various parameters. The soil pH was determined in 1:2.5 soil:water ratio using the pH meter with glass electrodes; electrical conductivity (µSc m -1 ) was determined 6 . The organic carbon in the soil was estimated by methods suggested by Walkley and Black 16 (1934); total N content by alkaline potassium permanganate 9 ; NaHCO 3 extractable P by spectrophotometer by flame photometer 13 .

Statistical Analysis
Analyses were performed indicating the relationship between soil physicochemical properties in high altitude region of GNP. To analyze the significant relationship between elevation and physicochemical properties (pH, electric conductivity, soil organic carbon, soil moisture, Nitrogen, and Phosphorus content), Kruskal Wallis analysis of variance (ANOVA) was performed with post hoc test (Dunn test, in FSA package with a critical significance level of 0.05). Spearman's correlation analysis was used between elevation and various soil parameters. All statistical calculations were performed in R platform.

Results
The results showed that the GNP soils were sandy loam in texture. The soil in the park was mainly composed of sand (83.8%) followed by clay (16.17%) and a negligible amount of silt (0.02%). The mean soil Nitrogen and Phosphorus content were calculated as 0.37 ± 0.02%, and 0.35 ± 0.02% respectively (Table 1).
Average Nitrogen content in the GNP soil range from 0.734% at lower elevation to 0.015% at upper elevation. The value of N first decreases along the elevation gradient expect a sudden rise in Nitrogen content at a mid   Table 2) the change in Nitrogen content were statistically significant (Kruskal Wallis test, p<0.05). The highest recorded mean value of Nitrogen content was 0.652 ± 0.01 (at 3100 -3200 masl) whereas there is no significant difference in Phosphorus content but decreased along the elevation. The value of available Phosphorus was highest (0.53 ± 0.03) at lower elevation range 3200-3300 masl and lowest (0.19 ± 0.01) at the highest elevation 3800-3900 masl ( Table 2) (Figure 1d). The soil in the GNP forest was found to be acidic in nature. Soil pH value ranged from 5.00 -6.28. Acidity at the mid-elevation range statistically differs at altitudinal range 3300 -3500m (Figure 1e). Electrical Conductivity (EC) showed the same pattern as pH, decreased along the elevation gradient expect at elevation range 3300 -3400 ( Figure 1f).
Soil organic carbon and soil moisture were higher in lower altitudes as compared to the higher altitudes where cold and dry climate prevails and the soil remains devoid of any vegetation cover most of the time (Figure 1a, 1b). The correlation analysis among the different soil parameters showed that SOC has significant positive correlations with Nitrogen (correlation coefficient r = 0.76, p<0.05), and soil moisture (r = 0.60, p<0.05) ( Table  2). Soil organic carbon, soil moisture and Nitrogen content were negatively correlated and significantly differs with the elevation (Figures 2, 3, 4).

Discussion
The soil in the park was sandy loam and acidic in nature. No particular pattern of acidity has been established with elevation. However, SOC and soil moisture increases at the middle elevation (3400m -3500 m and 3700 m -3800 m) and further decreases along the elevation which may be due to human disturbance in the form of camping spot for trekkers at this elevation and presence of mixed forest     (subalpine deodar, pine and birch) at 3400 m -3500 m elevational range. The mid-elevation mixed subalpine forest harbors dense vegetation cover of deodar, betula and blue pine. The soil was dark in comparison with the color patterns of samples collected from higher elevations. The quantity of N and P is higher at lower to mid elevation may be due to the crowed canopy of subalpine vegetation and presence of preferred amount of soil nutrients 14 . Among various elevation range, there is a comparatively good amount of Phosphorus content in birch dominated area at mid elevation range (3500 m -3800 m) than the other vegetation occupied region along the elevation. This result conforms to the study done in Nanda Devi biosphere reserve forest 15 . The correlation analysis indicated that the soil of this area was also rich in nutrients such as Nitrogen and phosphorous at lower elevation where vegetation prevails below tree line up to 3800 m elevation range. The nutrient content of the soil changes along with the changes in temperature as it is Assessment of Soil Physicochemical Properties along... dependent on the decomposition of organic matter. Thus, any future increment in the temperature of this region may increase the soil's organic carbon and nutrients such as Nitrogen and phosphorous. On the other hand, soil samples collected from high altitudes (>3500 m) significantly lacks SOC and soil nutrients except from at 3400 m -3500 m and 3700 m -3800 m. This may be explained as the impact of long term human influence in the forms of camping and altering the natural habitat.
As an example, the famous trekking destination and pilgrimage site of Chirwasa and Bhojbasa are situated in this range. Soil moisture and soil organic carbon decreases along the elevation, it may be due to lesser or no tree crown cover, harsh weather conditions at higher altitude of alpine region above tree line i.e >3800 m where dry alpine scrub artemisia is prevalent. This provides the baseline trend of soil parameter in the study area.

Conclusion
The present study in the Gangotri National Park (GNP) focused on the availability of nutrients in soils along the altitude gradient. Vegetation shifts from lower elevation sub alpine deodar, blue pine, birch dominated forest to alpine scrub at high elevation range which results in change in soil macronutrient properties. The lower to middle altitude of GNP contains significantly increased SOC, macronutrients KMnO 4 -N, Olsen-P, NH 4 OAc-K and soil moisture as compared to high altitude ranges. There was a trend of increment in Soil Organic Carbon, Nitrogen and Phosphorus content due to shifting from higher to the lower altitude of the ecosystem. Finally, there was significant negative correlation of SOC, TN and soil moisture with elevation while the positive correlation between soil organic carbon, Nitrogen content and soil moisture was observed. Improvement in SOC build-up and soil macro-nutrients along with altitudes ranged were significant findings of the ecosystem. Therefore, this study may further help in climate change study in the current scenario of global warming in relation with above ground vegetation and underground soil biota to understand the soil food web dynamics. Further research is required to extrapolate (from the small ecosystem to a large Indian Himalayan extent) these altitude based nutrient availability and the concept (shifting of nutrient from higher to lower altitude).