Effect of Canopy Cover of Capparis decidua Forsk. on Soil Conditions in Thal Desert

Desert shrubs have a deep root system which allows them to explore the soil minerals and moisture from deeper horizons of soil and strongly support the local dwellers’ livelihoods. Capparis decidua (Forsk.) Edgew, generally known as karir, a xerophytic, densely branched shrub, is widely found in arid and semi-arid areas of Pakistan. The present study was conducted at four different sites in the Thal desert to determine the canopy effect of C. decidua on soil nutrients. Soil nutrients under the plant canopy (UC), at a distance of 150 cm away from the canopy (D150) and 300 cm away from the canopy area (D300) were determined. Data revealed that the soil nutrient status was higher in UC soils than the soils of (D150) and (D300). Levels of soil NPK in UC soil vs soils of D150 and D300 was: Nitrogen (N) = 0.49% vs 0.41% & 0.34%; Phosphorus (P) = 7.2 mg/L vs. 6.1 mg/L & 5.3 mg/L; Potassium (K) = 104 mg/L vs 91 mg/L & 83 mg/L. Similarly, soil organic matter (OM) = 1.25% vs 1.05% & 0.83%; sulphur (S) = 8.75 mg/L vs. 8.09 mg/L & 7.19 mg/L. Conversely, carbonates (CO 3-- ), Bicarbonates (HCO 3- ), and pH were lowest in UC soil, as values of CO 3--, HCO 3- and pH in UC soil were < D150 < D300. The noted values of CO 3-- in UC soil (0.52 meq/L) < D150 soils (0.67 meq/L) < D300 soils (0.94 meq/L); HCO 3- in UC soil (42.80 meq/L) < D150 soils (45.85 meq/L) < D300 soils (53.10 meq L- 1 ); pH - in UC soil (7.19) < D150 soils (7.26) < D300 soils (7.41) explained well this pattern. It was concluded that C. decidua improved the nutrient deprived sandy soils by enhancing the soil nutrient level.


INTRODUCTION
Rangelands are a variety of lands which support natural flora like shrubs, grasses, and forbs, and provide habitats both to local flora and fauna which have soaring worth for both recreation and scientific use. Rangelands cover almost 50% of the biosphere and provide around 70% of feeding essentials of native ruminants worldwide (Holechek et al., 1998;Friedel et al., 2000).
The total area of Pakistan is about 79.6 million hectares, out of which 65.6% (52.2 million hectares) is under rangelands. Only 18.5 million hectares is cultivated and used for livestock browsing and grazing (Quraishi, 2005). For sustaining the environmental solidity in the country, range flora is of prime importance (Sultani et al., 1985). Range areas of Pakistan are providing 40-60% of the fodder requirements for different types of livestock. Because of the severe land degradation and increase in drought, the production of range areas in Pakistan has dropped to 10-50% of their prospective yield (Quraishi, 2005).
Trees and shrubs of dry regions play a very important role in the enrichment of nutrient poor sandy soil. Their ethno-botanical services are of sustainable significance in view of improving the low nutrient status of the sandy soil (Kellman, 1979;Belsky et al., 1989; Bargali and Bargali, 2009). Capparis decidua (Forsk.) Edgew (Capparaceae), commonly known as Karir, is a drought tolerant shrub found in arid areas of Pakistan as compact bunches (Gupta, 2010). Along with numerous socioeconomic and environmental benefits (Mahla et al., 2010), all parts of the plant have been used in many medicines all over the world. The spicy-tasting fruits serve as an astringent for bowels, a remedy for bad breath and a possible cure for cardiac troubles (Sharma et al., 2011). The green young pods are used as anthelminthic and laxatives, and are active in the treating of asthma, constipation, coughs, as well as hysteria and other mental disorders (Ghazanfar, 1994). In many parts of the world, the faded fruit is cooked (Agarwal et al., 1988). Green berries are used in manufacturing pickles used as food in some countries (Sharma et al., 2011).
The effects of individual trees and shrubs on such soil have been investigated by many scientists in a wide variety of ecosystems. A lot of research work has been done on the ethnobotanical characters of this species. However, little research work regarding the soil plant interaction of C. decidua has been done so far. In view of the above discussion, the present study was conducted to find out the role of C. decidua in soil enrichment by quantifying differences in soil nutrient status under the plant canopy (UC), at 150 cm away from the canopy (D-150) and 300 cm away from the canopy (D-300).

MATERIALS AND METHODS
The Thal desert covers an area of about 2.5 million hectares and comprises the districts Bhakker, Mianwali, Layyah, Muzzafargarh, Khoshab, Sargodha and Jhang. Annual precipitation of the area is between 150 to 200 mm at 31-33 o N latitude and 71.07 o E at an altitude of 200 meters. The area experiences cold winters and severe, hot summers with temperatures between 0 o C to 44 o C annually. Soil erosion is experienced in many parts of the Thal desert because of strong winds that blow frequently. The soil is moderately calcareous, with alkaline clay loam and alluvial with a sandy texture (Muhammad, 1989;Quraishi et al., 2006). The main vegetation of the Thal range area consists of shrubs and grasses rather than trees. Common shrubs of this desert are Capparis decidua (Karir), Acacia jacquemontii (Babble acacia), Calligonum polygonoides (Phog), Capparis aphylla (Karir), Haloxylon recurvum (Lana), Prosopis cineraria (Jand), Solvadora oleoides (Van), and Tamarix aphylla (Farash), (Quraishi et al., 2006).
The study was conducted at various range sites of the Thal rangeland, i.e Rakh Chobbara, Rakh Kherewala (Layyah), Rakh Dagarkotli (Bhakker). At each site, 10 large shrubs of Capparis decidua were randomly selected and tagged. Soil samples in the cardinal directions of each selected shrub were collected with the help of soil augar. The first soil sample was collected under the shrub canopy beside the stem at a soil depth of 15 and 30 cm. The 2 nd and 3 rd soil samples were collected at a distance of 150 cm and 300 cm away from the canopy of the selected shrub at the same soil depth and mixed together to form a composite sample for further chemical analysis. The tagged samples were taken to the soil testing laboratory for soil analysis using the standard protocol outlined by Okalebo et al. (2002). Value of various parameters like soil organic matter, moisture contents, Nitrogen (N), Phosphorous (P), Potassium (K), Electrical conductivity (EC), Carbonates (CO3 --), Bicarbonates (HCO3 -), Chlorides (Cl) and soil pH were assessed. The mean values of these parameters under various soil regimes (as mentioned above) were compared for their statistical significance using Fisher's LSD test at a 5% probability level. The correlations between various soil property values were determined using the Pearson's linear correlation coefficient.

Soil Organic Matter (OM%)
Presence of soil organic matter (OM) is the major indication of soil fertility, as it is the only source of soil nitrogen. According to an estimate, one ton of OM adds about 50 kg of N and 5 kg of P and S each to the soil. According to another estimate, in soil organic matter C:N:P:S = 100:10:1:1. Generally speaking, organic matter carrying 8-12 kg of C also contains 1 kg nitrogen (Allison, 1973). Figure 1 depicts organic matter (%) in the soil of Capparis decidua collected from 3 different (randomly selected) sites of the Thal desert in the Punjab Province (Pakistan). Data revealed that the maximum value of OM (1.25%) was found in under canopy (UC) soils, followed by its significant decrease (1.05% and 0.83%) from canopy area to 150 cm (D-150) and 300 cm (D-300) away from the plant canopy. For instance, the higher level of OM in the soils from UC than the soils of D-150 and D-300 showed enhanced fertility levels in UC soils under the canopy of Capparis decidua plants. Noureen et al. (2008) also found relatively higher levels of OM in the UC soils of C. polygonoides. It is obvious from the results that UC soils of C. polygonoides had more organic matter and it was gradually decreased while moving away from the canopy ( Figure 1).  Arshad et al. (2008) described the same results while working on Aerva javanica, Dipterygium glaucum, Calligonum polygonoides, Haloxylon salicornicum and Capparis decidua. They reported a significant increase in the OM of the UC soils of the experimental plants than the soils located away from canopy. Data reliability was assessed using statistical indicators such as the coefficient of variance (CV) 0.79%, significance among various means of soil OM (at p < 0.05) and the least significant difference (LSD) value (0.17) to compare means with standard error (0.081).

Soil Nitrogen (N%)
Nitrogen (N) is the most claimed inorganic nutrient by plants among all other nutrients. The ratio of N and C in soils usually differ from 10 to 15 times or somewhat greater, and is comparable to that of the N:P ratio as declared above (Allison, 1973). The mean nitrogen (N) content recorded in the sampled soil of the experimental area is shown in Figure 2. significantly decreased in the soils of D-150 (0.41%), followed by D-300 (0.34%).
Results proved that C. decidua showed higher levels of N in UC soils and the level of N was gradually decreased while moving away from the canopy area. The gradual decrease in N levels, while moving away from the canopy area, clearly suggested that the role of C. decidua at the site is synergetic to improve the soil fertility. Noureen et al. (2008)

Soil Phosphorous (P mg/L)
After N, the most limiting available macronutrient for plant growth is P. Phosphorous is of great importance, building up roughly 0.2% of a plant's dry biomass. It is a constituent of basic molecules, such as nucleic acids, phospholipids, and ATP, and, therefore, plants cannot grow without a consistent supply of this mineral nutrient (Theodorou and Plaxton, 1993). It is noteworthy to mention that 20 to 80% of P in soils is present in the organic form, of which phytic acid (inositol hexaphosphate) is generally a main constituent (Richardson, 1994). The rest is present as an inorganic portion comprising about 170 mineral forms of P (Holford, 1997). Obviously, the organic phosphorus compounds are more resistant to biological attacks than are the organic nitrogen and sulfur compounds Mean phosphorous (P) concentration noted in the soils of various experimental sites is shown in Figure 3. Haque (1992) and Radaei (2014) are also in agreement with the findings of this study, which explained that the soils of open areas, i.e. away from the base of C. decidua plants' influence, is deficient in available P. They stated that P content decreased significantly as the distance from the tree bole increased, getting away from the canopy. Table 1 shows significance among various means of P in Capparis decidua with CV (4.46%) at p < 0.05 with LSD value (0.049) and standard error (0.023) for different means.

Soil Potassium (K mg/L)
Potassium is the most ample cation in the cells of non-halophytic vascular plants (Maathuis et al., 1997). It is usually the most abundant of the major nutrient elements in soil. The total K content of soils varies from < 0.01% to about 4% and is commonly about 1% (Wild, 1988). Mean contents of K observed in all replicates of the experimental sites is incorporated in Figure 4. This study showed that under canopy soils had higher contents of K in the above mentioned soils as compared to soils away from canopy. For instance, the decreasing order of K levels found in the soils of UC of the plant vs. D-150 and D-300 was: 104.0 mg/L vs 91 mg/L and 83 mg/L. Githae et al. (2011) studied the canopy effect of Acacia senegal and found higher K levels under the canopy soils as compared to open area. The reason behind the high concentration of K under the canopy rather than in open areas might be high organic matter accumulation, decomposition and releases in the soil (Brady and Weil, 2002;Holdo and Mack, 2014). Table 1 shows reasonably low CV% (1.08) and standard error (0.052), and recommends that the noted data regarding potassium was highly reliable to interpret the results on a statistical basis at p <0.05 with the LSD value (0.11) for different means.

Soil Sulphur (S mg/L)
Sulphur (S) is an essential element that is required in larger amounts than is generally supposed.
Conservative estimates indicate that 50-70% of the sulfur of soils is in the organic matter. Most of the sulfur is present in the organic matter or adsorbed on it. Where the sulfur supply is deficient, plant growth may be markedly retarded (Allison, 1973). The mean contents of S (mg/L) recorded in the experimental soils is shown in Figure 5. Data revealed that the UC soil of C. decidua ranked at the top with regard to S concentration in the soil. The same was gradually decreased in the remaining two soils (D150 and D300) while moving away from the plant canopy. The decreasing order of S levels found in UC soils (12.08 mg/L) was > S levels in the soils of D150 (10.42 mg/L) > soils of D300 (8.57 mg/L). Table 1 describes the importance and significance (p < 0.05) between several means of S in C. decidua at all 4 sites with LSD values of 0.049, CV% of 3.02 and standard error of 0.045 for different means. Blank and Derner (2004) Jafari et al. (2003) while working in Hoz-e-Soltan of Qom province, Iran, on the soil-Plant relationship. They described higher levels of Sulphur in under canopy soils.

Level of Carbonates (CO3 -meq/L)
The Carbonates present in soil can disturb soil production by manipulating soil pH, structure, water holding capacity and H2O movement. They can alter soil structure by modifying the texture and amending the aggregation of soil particles (McCauley et al., 2005). The critical C:S ratio in carbonaceous materials above which immobilization occurs rather than mineralization has been reported to be approximately 50: 1 (C:N ratio = 5), but this ratio will vary widely depending on the nature of the carbon source (Allison, 1973). The mean CO3 -concentration recorded in the soils of experimental sites is shown in Figure 6.  cover of Capparis decidua was determined using LSD value of (0.087).

Level of Bicarbonates (HCO3meq/L)
HCO3is an essential component involved in plant growth on calcareous soils (Woolhouse, 1966a). Its existence in a larger quantity has adverse effects on the preoccupation of ions and results in chlorosis in plants (Brown, 1961). High levels of HCO3in soils and water appear to prevent the metabolic development of vegetation, which eventually disturbs the vegetal development and the endorsement of nutrient minerals (Dogar et al., 1980).
The mean HCO3concentration recorded in the soils of all experimental sites is shown in Figure 7. Noureen et al, (2008) also found relatively, higher levels of HCO3in the soils away from the canopy as compared to under canopy soils. Relatively less CV% (0.79) with a standard error (0.01) and LSD (0.023) explored that data regarding HCO3levels in the field for different means as influenced by the canopy cover of Capparis decidua was reliable at p < 0.05.

Soil pH
The mean pH of the soil collected from 4 sites is given in Figure 8. Highest pH values were recorded in open areas, i.e. at 300 cm and 150 cm away from canopy cover in all above mentioned sites, as compared to under the canopy. The decreasing order of pH levels found in the soils D-300 vs. D-150 and UC soils at various sites was: pH of D-300 soils (7.41) > pH of D-150 soils (7.26) > pH (7.19) of UC soils. Analysis of variance yielding CV% (1.05) with a standard error of (0.053) and LSD value of (0.11) for different means showed data reliability concerning soil pH as influenced by the canopy cover of Capparis decidua. Leonard and Field (2003)