Agroforestry has the potential to enhance climate change adaptation. While benefits from agroforestry systems consisting of cash crops and shade trees are usually attributed to the (shade) trees, the trees can also have negative impacts due to resource competition with crops. Our hypothesis is that leaf phenology and height of shade trees determine their seasonal effect on crops. We test this hypothesis by categorizing shade tree species into functional groups based on leaf phenology, shade tree canopy height and shade tree light (wet and dry season) interception as well as the effects. To this end, leaf phenology and the effects on microclimate (temperature, air humidity, intercepted photoactive radiation (PAR)), soil water, stomatal conductance and cocoa yield were monitored monthly during wet and dry seasons over a two-year period on smallholder cocoa plantations in the northern cocoa belt of Ghana. Seven leaf phenological groups were identified. In the wet season, highest buffering effect of microclimate was recorded under the trees brevi-deciduous before dry season. During dry season, high PAR and lowest reduction in soil moisture were observed under the trees in the group of completely deciduous during dry season. The evergreen groups also showed less reduction in soil water than the brevi-deciduous groups. In the wet season, shade tree effects on cocoa tree yields in their sub canopy compared to the respective control of outer canopy with full sun ranged from positive (+10 %) to negative (-15 %) for the deciduous groups, while yield reductions for the evergreen groups ranged from -20 % to -33 %. While there were negative yield impacts for all phenological groups in the dry season, the trees in completely deciduous during dry season group recorded least penalties (-12 %) and the trees with evergreen upper canopy the highest (-35 %). The function of shade trees in enhancing climate resilience is therefore strongly dependent on their leaf phenological characteristics. Our study demonstrates how the key trait leaf phenology can be applied to successful design of climate-resilient agroforestry systems.

PurposeGrass pea (Lathyrus sativus L.) has significant nutritional value and broad-spectrum resistance properties. However, the neurotoxin beta-N-oxalyl-L-alpha, beta-diaminopropionic acid (beta-ODAP) in its seeds increases exponentially during drought stress, and overconsumption can lead to neurogenic hypoparalysis. Superabsorbent polymer (SAP) has the potential to improve soil physicochemical properties and alleviate plant drought stress, but the effects of different SAP concentrations on soil water availability, physiological traits, and beta-ODAP content of grass pea under drought conditions are unclear. The objective of this study was to elucidate the impact of SAP on the physiological and biochemical characteristics, as well as the beta-ODAP content, of grass pea under drought conditions.MethodsWe conducted potting experiments of natural drought with L. sativus cv. Wugong Yongshou (WGYS), L. sativus cv. Jingbian (JB), L. sativus cv. Aksu (AKS), and cultivated grass pea (ZP) materials with different SAP ratios (0.00%, 0.25%, 0.50%, 0.75%, 1.00%).ResultsThe research confirmed that the addition of 0.50% SAP had a positive effect on soil physicochemical properties and growth parameters of grass pea, including plant height, leaf area, leaf water potential, seed yield, and straw yield per plant; Following an eight-day cessation of irrigation, the transpiration rate (E), stomatal conductance (GH2O), intercellular CO2 concentration (Ci), and net photosynthetic rate (A) of the four grass pea leaves exhibited a notable optimization in comparison to the control without SAP; The levels of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), malondialdehyde (MDA), and beta-ODAP (leaves, seeds, and straw) of four grass pea plants treated with 0.50% SAP were significantly decreased.ConclusionSAP can improve soil water-holding capacity, leaf photosynthesis to alleviate oxidative damage caused by drought stress in grass pea, reduce beta-ODAP content, and promote low-toxicity and high-yield planting.

The impact of biochar application on plant performance under drought stress necessitates a comprehensive understanding of biochar-soil interaction, root growth, and plant physiological processes. Therefore, pot experiments were conducted to assess the effects of biochar on plant responses to drought stress at the seedling stage. Two contrasting maize genotypes (drought-sensitive KN5585 vs. -tolerant Mo17) were subjected to biochar application under drought stress conditions. The results indicated that biochar application decreased soil exchangeable Na+ and Ca2+ contents while increased soil exchangeable K+ content (2.7-fold) and electrical conductivity (4.0-fold), resulting in an elevated leaf sap K+ concentration in both maize genotypes. The elevated K+ concentration with biochar application increased root apoplastic pH in the drought-sensitive KN5585, but not in the drought-tolerant Mo17, which stimulated the activation of H+-ATPase and H+ efflux in KN5585 roots. Apoplast alkalinization of the drought-sensitive KN5585 resulting from biochar application further inhibited root growth by 30.7%, contributing to an improvement in water potential, a reduction in levels of O2-, H2O2, T-AOC, SOD, and POD, as well as the down-regulation of genes associated with drought resistance in KN5585 roots. In contrast, biochar application increased leaf sap osmolality and provided osmotic protection for the drought-tolerant Mo17, which was associated with trehalose accumulation in Mo17 roots. Biochar application improved sucrose utilization and circadian rhythm of Mo17 roots, and increased fresh weight under drought stress. This study suggests that biochar application has the potential to enhance plant drought tolerance, which is achieved through the inhibition of root growth in sensitive plants and the enhancement of osmotic protection in tolerant plants, respectively. Biochar application decreased soil exchangeable Na+ and Ca2+, but increased soil exchangeable K+ and electrical conductivity.Biochar increased apoplastic pH, but reduced root growth, stress damage and stress response during drought for the drought-sensitive KN5585.Biochar improved osmotic protection, trehalose accumulation, and fresh weight during drought for the drought-tolerant Mo17.