Unraveling the impact of human perturbation on nitrogen cycling in terrestrial ecosystems of lower Himalaya, Pakistan.

Terrestrial ecosystems are under the enormous pressure of land use management regimes through human disturbances, resulting in the disruption of biogeochemical cycles and associated ecosystem services. Nitrogen (N) in soil ecosystems is of vital importance for primary productivity, hence estimating the extent of these human interventions on N-cycling processes becomes imperative from economic and environmental perspectives. This work investigated the impacts of variable anthropogenic activities on N cycling in three different terrestrial ecosystems (arable, grassland, and forest) in three regions of lower Himalaya, Pakistan. Potential nitrification (PNA) and denitrification (DEA) enzyme activities, relative distribution of inorganic N species (NH4, NO3), and the role of inherent edaphic factors were assessed. Results revealed high nitrification potentials and increased nitrous oxide (N2O) emissions in the incubated soil microcosms, in the order as arable > grassland > forest ecosystems. Notably, higher rates of both studied processes (~ 30-50%) and elevated soil mineral nitrogen pool were observed in arable ecosystems. Forest soils, assumed as pristine ecosystems relying mainly on natural N fixation, produced (de)nitrification rates relatively lower than grasslands, followed by arable soils which were moderately disturbed through long-term fertilization and intensive land-use regimes. Linear regression modeling revealed that the inorganic N species (particularly NO3), and inherent edaphic factors were the key determinants of high (de)nitrification rates, hence warn of accelerated N losses in these ecosystems. The study highlights that elevated PNA and DEA being proxies for the altered N cycling in the studied terrestrial ecosystems are of great ecological relevance in view of predicted N2O budget in the lower Himalaya.

Differential Effect of Heat Stress on Drought and Salt Tolerance Potential of Quinoa Genotypes: A Physiological and Biochemical Investigation.

Soil salinity, drought, and increasing temperatures are serious environmental issues that drastically reduce crop productivity worldwide. Quinoa (Chenopodium quinoa Willd) is an important crop for food security under the changing climate. This study examined the physio-biochemical responses, plant growth, and grain yield of four quinoa genotypes (A7, Titicaca, Vikinga, and Puno) grown in pots containing normal (non-saline) or salt-affected soil exposed to drought and elevated-temperature treatments. Combinations of drought, salinity, and high-temperature stress decreased plant growth and yield more than the individual stresses. The combined drought, salinity, and heat stress treatment decreased the shoot biomass of A7, Puno, Titicaca, and Vikinga by 27, 36, 41, and 50%, respectively, compared to that of control plants. Similar trends were observed for grain yield, chlorophyll contents, and stomatal conductance. The combined application of these three stresses increased Na concentrations but decreased K concentrations in roots and shoots relative to control. Moreover, in the combined salinity, drought, and high-temperature treatment, A7, Puno, Titicaca, and Vikinga had 7.3-, 6.9-, 8-, and 12.6-fold higher hydrogen peroxide contents than control plants. All four quinoa genotypes increased antioxidant enzyme activities (CAT, SOD, and POD) to overcome oxidative stress. Despite A7 producing the highest biomass under stress, it did not translate into increased grain production. We conclude that Puno and Titicaca are more tolerant than Vikinga for cultivation in salt-affected soils prone to drought and heat stress.

Salinity mitigates cadmium-induced phytotoxicity in quinoa (Chenopodium quinoa Willd.) by limiting the Cd uptake and improved responses to oxidative stress: implications for phytoremediation.

Cadmium (Cd) contamination and soil salinity are the main environmental issues reducing crop productivity. This study aimed to examine the combined effects of salinity (NaCl) and Cd on the physiological and biochemical attributes of quinoa (Chenopodium quinoa Willd.). For this purpose, 30-day-old plants of quinoa genotype "Puno" were transplanted in Hoagland's nutrient solution containing diverse concentrations of Cd: 0, 50, 100, 200 µM Cd, and salinity: 0, 150, and 300 mM NaCl. Results demonstrated that plant growth, stomatal conductance, and pigment contents were significantly lower at all Cd concentrations than the control plants. Quinoa plants exhibited improved growth and tolerance against Cd when grown at a lower level of salinity (150 mM NaCl) combined with Cd. In contrast, the elevated concentration of salinity (300 mM NaCl) combined with Cd reduced shoot and root growth of experimental plants more than 50%. Combined application of salinity and Cd increased Na (25-fold), while lessened the Cd (twofold) and K (1.5-fold) uptake. A blend of high concentrations of Na and Cd caused overproduction of H2O2 (eightfold higher than control) contents and triggered lipid peroxidation. The activities of antioxidant enzymes: ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) were 13, 12, 7 and ninefold higher than control to mitigate the oxidative stress. Due to restricted root to shoot translocation, and greater tolerance potential against Cd, the quinoa genotype, Puno, is suitable for phytostabilization of Cd in saline soils.

Effects of arsenite on physiological, biochemical and grain yield attributes of quinoa (Chenopodium quinoa Willd.): implications for phytoremediation and health risk assessment.

The objectives of this study were to investigate the effects of arsenic (As) on physiological and biochemical attributes of quinoa, and human health risks associated with the consumption of As contaminated grains of quinoa. Quinoa genotype, Puno was grown on soil contaminated with various levels of arsenite; 0, 10, 20, 30, and 40 mg As kg-1 soil. Results revealed that plant growth, photosynthetic pigments, stomatal conductance, and grain yield of As treated plants were significantly less as compared to control plants. Plants exposed to elevated levels of 30 and 40 mg As kg-1 of soil could not survive until maturity. Plant roots retained higher concentration of As than shoot indicating As phytostabilizing behavior of quinoa. Arsenic toxicity caused oxidative stress in quinoa plants, which elevated the H2O2 and TBARS contents and decreased membrane stability. This oxidative stress was partly mitigated by the induction of antioxidant enzymes (SOD, CAT, POD, APX). Perhaps, our results regarding As availability might be an overestimate of the typical natural conditions, As accumulation in quinoa grains posed both carcinogenic and non-carcinogenic health risks to humans. It was concluded that quinoa is sensitive to As and the consumption of quinoa grains from plants grown on As concentration ≥20 mg kg-1 of soil was not safe for humans. Novelty statement: The tolerance potential of quinoa (Chenopodium quinoa Willd.) against the trivalent form of arsenic (arsenite), and the health risks due to the consumption of arsenic-contaminated grains has not been explored yet. This is the first study in which we have explored the effects of arsenite on physiological, biochemical and phytoremedial attributes of quinoa. Moreover, human health risks associated with the consumption of As contaminated grains of quinoa has have been investigated. The findings of the present study would be helpful for farmers who intend to grow quinoa on arsenic-contaminated soils.

Effect of salinity on physiological, biochemical and photostabilizing attributes of two genotypes of quinoa (Chenopodium quinoa Willd.) exposed to arsenic stress.

Soil salinity and arsenic (As) contamination are serious environmental problems. To investigate the effects of salinity on As uptake and physiological and biochemical attributes of quinoa (Chenopodiumquinoa Willd.), a hydroponic experiment was performed. One-month old healthy plants of two quinoa genotypes; Vikinga and A7 were transplanted in plastic tubs containing half strength Hoagland's nutrient solution. Plants were exposed to different levels of As (0, 150 and 300 µM), salinity (0, 150 and 300 mM) and their combinations (150 µM As + 300 mM NaCl; 300 µM As + 300 mM NaCl) for five weeks. Results revealed that combined application of salinity and As caused more pronounced reduction in growth, chlorophyll contents and caused more oxidative damage in both quinoa genotypes. Under combined application of salinity and As, Na+ concentration was increased whereas As content was decreased in plant tissues. Quinoa genotype A7 was more tolerant than Vikinga against salinity, As and their combination perhaps because of less uptake of toxic ions and higher activities of antioxidant enzymes (SOD, CAT, POD). Bioconcentration factor (BCF), translocation factor (TF) and tolerance index (TI) indicated that genotype A7 can be successfully employed for phytostabilization of As contaminated saline soils.

Assessment of flood-induced changes in soil heavy metal and nutrient status in Rajanpur, Pakistan.

Flood events around the globe have severely impaired the soil functioning resulting in compromised food security in several parts of the world. The current study was aimed to explore the impacts of floods on soil heavy metals and nutrients status at three locations; Tibbi Solgi (TS), Vinri Khosa (VK), and Noshehra West (NW-control) in the district Rajanpur of Punjab, Pakistan. TS and VK sites were under regular influence of flooding over the last many years, but no flood event was reported on NW site during the same tenure; hence, it served as control. Sampling was carried out before and after flooding on the experimental sites. Vegetation cover was monitored through remote sensing techniques. Results revealed varying effects of floods on soil heavy metals; Cd, Cr, Pb, and soil phosphorous and nitrates. Flood events increased the Cd while lowered Pb concentration at VK site; however, flooding did not influence the status of Cr in soil. Similar to the trend observed in case of Cd, soil phosphorous and nitrates were reduced after flood events. Correlation analyses of soil physicochemical properties with soil heavy metals and nutrients indicated that after flood events, soil texture and organic carbon content seem to be the major factors driving the shift in soil heavy metals and nutrient concentrations. Although pollution indices indicated a marginally low contamination levels, but as projected in empirical studies, regular flood events in the studied sites may contaminate the whole ecosystem rendering it unfit for agricultural productivity.

Integrated phytobial heavy metal remediation strategies for a sustainable clean environment - A review.

Heavy metal contamination in the environment is a global threat which accelerated after the industrial revolution. Remediation of these noxious elements has been widely investigated and multifarious technologies have been practiced for many decades. Phytoremediation has attracted much attention from researchers. Under this technology, heavy metal hyperaccumulator plants have been extensively employed to extract extraordinary concentrations of heavy metals but slow growth, limited biomass and stresses caused by heavy metals imperil the efficiency of hyperaccumulators. Plant growth promoting rhizobacteria (PGPR) can help overcome/lessen heavy metal-induced adversities. PGPR produce several metabolites, including growth hormones, siderophores and organic acids, which aid in solubilization and provision of essential nutrients (e.g. Fe and Mg) to the plant. Hyperaccumulator plants may be employed to remediate metal contaminated sites. Use of PGPR to enhance growth of hyperaccumulator plant species may enhance their metal accumulating capacity by increasing metal availability and also by alleviating plant stress induced by the heavy metals. Combined use of hyperaccumulator plants and PGPR may prove to be a cost effective and environmentally friendly technology to clean heavy metal contaminated sites on a sustainable basis. This review discusses the current status of PGPR in improving the growth and development of hyperaccumulator plants growing in metal contaminated environments. The mechanisms used by these rhizosphere bacteria in increasing the availability of heavy metals to plants and coping with heavy metal stresses are also described.

Determination of lytic enzyme activities of indigenous Trichoderma isolates from Pakistan.

This study investigated lytic enzyme activities in three indigenous Trichoderma strains namely, Trichoderma asperellum, Trichoderma harzianum and Trichoderma sp. Native Trichoderma strains and a virulent strain of Rhizoctonia solani isolated from infected bean plants were also included in the study. Enzyme activities were determined by measuring sugar reduction by dinitrosalicylic acid (DNS) method using suitable substrates. The antagonists were cultured in minimal salt medium with the following modifications: medium A (1 g of glucose), medium B (0.5 g of glucose + 0.5 g of deactivated R. solani mycelia), medium C (1.0 g of deactivated respective antagonist mycelium) and medium D (1 g of deactivated R. solani mycelia). T asperellum showed presence of higher amounts of chitinases, ß-1, 3-glucanases and xylanases in extracellular protein extracts from medium D as compared to medium A. While, the higher activities of glucosidases and endoglucanses were shown in medium D extracts by T. harzianum. ß-glucosidase activities were lower compared with other enzymes; however, activities of the extracts of medium D were significantly different. T. asperellum exhibited maximum inhibition (97.7%). On the other hand, Trichoderma sp. did not show any effect on mycelia growth of R. solani on crude extract.

Determination of lytic enzyme activities of indigenous Trichoderma isolates from Pakistan

Abstract This study investigated lytic enzyme activities in three indigenous Trichoderma strains namely, Trichoderma asperellum, Trichoderma harzianum and Trichoderma sp. Native Trichoderma strains and a virulent strain of Rhizoctonia solani isolated from infected bean plants were also included in the study. Enzyme activities were determined by measuring sugar reduction by dinitrosalicylic acid (DNS) method using suitable substrates. The antagonists were cultured in minimal salt medium with the following modifications: medium A (1 g of glucose), medium B (0.5 g of glucose + 0.5 g of deactivated R. solani mycelia), medium C (1.0 g of deactivated respective antagonist mycelium) and medium D (1 g of deactivated R. solani mycelia). T asperellum showed presence of higher amounts of chitinases, β-1, 3-glucanases and xylanases in extracellular protein extracts from medium D as compared to medium A. While, the higher activities of glucosidases and endoglucanses were shown in medium D extracts by T. harzianum. β-glucosidase activities were lower compared with other enzymes; however, activities of the extracts of medium D were significantly different. T. asperellum exhibited maximum inhibition (97.7%). On the other hand, Trichoderma sp. did not show any effect on mycelia growth of R. solani on crude extract.

Effect of zinc and glucosinolates on nutritional quality of Noccaea caerulescens and infestation by Aleyrodes proletella.

The Zn hyperaccumulating plant, Noccaea caerulescens, was grown under controlled conditions at a range of Zn concentrations (0-1000 mg kg(-1) dwt. soil) to determine the effectiveness of hyperaccumulation in deterring the cabbage whitefly, Aleyrodes proletella, and to establish the relationship between levels of foliar Zn and glucosinolates (organic defence compounds). Two weeks after introducing A. proletella adults to the plants, next generation nymphs were quantified. This sucking insect caused minimal damage to plant tissue and did not affect foliar glucosinolate levels. Foliar Zn concentrations increased with increasing soil Zn application and reached a maximum of ~7000 mg kg(-1). More whitefly nymphs were observed on plants as the foliar Zn concentration increased (up to ~3000 mg kg(-1)) after which numbers declined. Zn was an explanatory variable in accumulated generalised linear regression after the variation in the data due to C/N ratio had been accounted for. Nymph numbers declined with increasing C/N ratio and increased with increasing N concentration. The highest glucosinolate concentrations were in shoots with the lowest Zn concentrations; this is consistent with the 'trade-off' hypothesis which states that elemental defence mechanisms allow for lowered organic defences.

Biocontrol efficacy of different isolates of Trichoderma against soil borne pathogen Rhizoctonia solani.

In this study, the biocontrol abilities of water-soluble and volatile metabolites of three different isolates of Trichoderma (T. asperellum, T. harzianum and Trichoderma spp.) against soil borne plant pathogen Rhizoctonia solani were investigated both in vitro and in vivo. The results showed for the first time that mycelial growth inhibition of the pathogen was 74.4-67.8% with water-soluble metabolites as compared to 15.3-10.6% with volatile metabolites in vitro. In vivo antagonistic activity of Trichoderma isolates against R. solani was evaluated on bean plants under laboratory and greenhouse conditions. We observed that T. asperellum was more effective and consistent, lowering disease incidence up to 19.3% in laboratory and 30.5% in green house conditions. These results showed that three isolates of Trichoderma could be used as effective biocontrol agents against R. solani.