Effects of soil and atmospheric drought on whole-tree transpiration (E_T), leaf water potential (Ψ_L) and whole-tree hydraulic conductance (K_T) were investigated in mature rubber trees (Hevea brasiliensis, clone RRIM 600) during the full canopy stage in the rainy season in a drought-prone area of northeast Thailand. Under well-watered soil conditions, transpiration was tightly regulated in response to high evaporative demand, i.e., above reference evapotranspiration (ET₀) ∼2.2 mm day⁻¹ or maximum vapor pressure deficit ∼1.8 kPa. When the trees experienced intermittent soil drought E_T decreased sharply when relative extractable water in the top soil was < 0.4. The midday leaf water potential (Ψ_md) on sunny days did not change as a function of soil drought and remained stable at approximately − 1.95 MPa, i.e., displaying isohydric behavior. The decrease in E_T was mainly due to the change in K_T. K_T remained constant over a wide range of environmental conditions and decreased sharply at low soil water availability. A simple hydraulic model incorporating critical minimum water potential and the response of whole-tree hydraulic conductance to relative extractable water correctly simulated patterns of transpiration over 6 months. We conclude that an explicit and simplified framework of hydraulic limitation hypothesis was sufficient to describe water use regulation of a mature rubber tree stand in water-limited conditions. Given the complexity of constraints in the soil–plant–atmosphere pathway, our results confirm the relevance of this approach to synthesize the overall behavior of trees under drought.

Organic amendments are believed to help increase the soil carbon storage and therefore improve soil quality, which may be important in the context of climate change. However, the added value of organic amendments for farmers must be clearly demonstrated in order to convince them of the utility of their use. The aims of this study were: (i) to investigate the impact on maize of compost and vermicompost combined with two levels (negligible and significant) of plant water stress; and (ii) to determine how the organic amendments affected the soil’s physical properties and maize productivity. Water stress levels were imposed by controlling the matric potential of soil columns in which cultivated soil characteristics was mimicked (10 cm topsoil with organic amendments, above a 50 cm subsoil without any inputs containing the majority of the roots). Plant and soil characteristics were monitored daily for 70 days. Our results show that the use of organic amendments is profitable for farmers as: (i) maize performances were increased in both moisture regimes; and (ii) the improvement was particularly striking in terms of yield. No additional benefits were measured when using vermicompost instead of compost. The data suggest that the improvement in plant characteristics did not result from increased water storage in the soils with organic amendments, but rather from better access to the water, resulting in faster root development in the macroporosity of the amended soils.

The Himalayan region is likely particularly exposed to climate change indicated by the high regional rate of change. The number of high-resolution, well-calibrated, and long-term paleoclimate reconstructions are however regrettably few, to set this change in a longer-term context. The dendroclimatic reconstructions over Himalaya that do exist have only reconstructed summer season temperatures, and rarely or never attempted to reconstruct mean annual temperatures. The paucity of long meteorological records is a matter of concern when developing chronologies of climate sensitive tree-ring data in Bhutan, but the chronologies would theoretically be of high potential for extending short meteorological records back in time using trees in high-elevation ecotones. The objectives of this study were to explore dendroclimatic signals in tree-ring width chronologies of Abies densa growing in these extreme ecotones and to reconstruct, if possible, annual temperatures over Northern Bhutan. A point-by-point regression analysis revealed that the regional composite chronology was significantly and positively correlated with temperatures of all months of the current year, i.e., January to December. The chronology was highly correlated with annual temperatures (calibration period R = 0.67 and validation period R = 0.50; p < 0.001) allowing a reconstruction of temperature over Northern Bhutan (NB-TEMR). The NB-TEMR reveals some common variations with summer temperature reconstructions of the Northern Hemisphere as well as the Himalayan region, particularly w.r.t to the recent warming trend. The reconstruction covers the period of 1765 to 2017. This reconstruction reveals a warming trend since 1850 with higher rates of warming 1935 to 2017, but with a pause around 1940–1970. The warming is consistent with reduced volcanic activity and increase of greenhouse gases. We anticipate that our new reconstruction of annual mean temperature could be an important contribution for future climate change studies and assessments of climate models.

The alpine treeline ecotones are an early indicator of vegetation’s response to changes in climate, and the advancement of diffuse treeline ecotones has been associated with mean annual warming temperatures. However, the knowledge of how tree demographic size, age and population distribution, and regeneration decrease with increasing elevation and mean annual temperature remain fragmentary in Bhutan. There was no explanation of how treelines migrate in response to the climate. Therefore, the objectives of this study were to investigate tree demographic size and age and population distribution, as well as the regeneration expansion of treeline ecotones of Abies densa trees in response to climate change. Demographic data from thirty transect bands from treeline ecotones and reconstructed mean annual temperatures from tree-rings were used. Regression analysis was used to establish a relationship between elevation/temperature and demographic tree size and age, as well as to determine recruitment frequency distributions and whether these could be driven by climate change. The tree demography indicated that the treeline ecotone in our sampling site is temperature limited. Hence, cooler temperatures at higher elevations should drive decreases in basal diameter, age and recruitment frequencies. From the dendroecological analysis, the diffuse treeline ecotones appear to be climbing on average 1.00 m per year in Northern Bhutan. We also found that the recruitment frequency has increased over recent years (1850–2017), as temperatures continue to rise. The thermal treeline ecotones will be likely to serve as a line of bioclimatic reference against which other zones of bioclimate can be defined. With documented responses of treeline ecotones toward mean annual temperatures, the expectation is that additional warming will continue to influence regeneration expansion in the future. This dynamic response of treeline ecotones towards the climate acts as an indicator of climate change. Information about climbing treelines and altered ecotones should be a vital part of the material for decision makers to consider, to assess impacts and threats to Himalayan alpine biota.

Durian (Durio zibethinus Murr.) is a major economic crop in Thailand, with the ‘Monthong’ cultivar being particularly valued for its commercial significance and extensive cultivation in northern Thailand. However, the thick, hard shell of durian complicates ripeness assessment based on external appearance, often leading to premature harvesting and unripe fruit sales. Variations in consumer preferences for different ripeness stages present challenges in meeting market demands. Due to the absence of a definitive harvest index for ‘Monthong’ durian, this study aims to (1) evaluate the potential of fruit shell color composition as an indicator of maturation stage and (2) assess the impact of harvest maturity on fruit quality and antioxidant content. A completely randomized design (CRD) was employed in the experiment. Fruits were collected at intervals of 15 days from 15 to 135 days after full bloom (DAFB). The results showed that fruit circumference and length increased progressively with age, with maximum fruit size observed at 90–135 DAFB. Fruit weight, firmness, dry matter, total phenolics, flavonoids, β-carotene, lycopene, and antioxidant activity peaked at 120 DAFB. The values recorded at this stage were: fruit weight (3652.30 g), firmness (42.08 N/cm²), dry matter (37.13%), total phenolics (43.98 mg/100 g fresh weight (FW)), flavonoids (8.33 mg catechin/100 g FW), β-carotene (1.35 mg/100 g FW), lycopene (53.98 mg/100 g FW), and antioxidant activity (6.32 mg TE/100 g FW). The highest total soluble solids (TSS) content was observed at 135 DAFB, with a value of 25 °Brix. These findings indicate that: (1) maturation stages can be effectively differentiated using shell color; (2) ‘Monthong’ durians reach their maximum size at 90 DAFB; (3) fruits harvested at 90–105 DAFB exhibit high firmness and low sweetness, making them suitable for markets prioritizing texture; (4) fruits harvested at 105–120 DAFB exhibit lower firmness and higher sweetness, making them preferable for direct consumption; and (5) total soluble solids, acidity, phenolics, flavonoids, β-carotene, lycopene, and antioxidant activity increase with maturation. These insights provide a valuable reference for optimizing harvest timing to meet specific market and consumer preferences.

Curcuma spp. is a popular ornamental crop valued for its vibrant appearance and suitability for both regular and off-season production. As global emphasis on freshwater conservation increases and with a demand for compact potted plants, reducing water use while maintaining high aesthetic quality presents a key challenge for horticulturists. Potassium silicate (PS) has been proposed as a foliar spray to alleviate plant water stress. This study aimed to evaluate the effects of PS on growth, ornamental traits, and photosynthetic parameters of off-season potted Curcuma cv. ‘Jasmine Pink’ under deficit irrigation (DI). Plants were subjected to three treatments in a completely randomized design: 100% crop evapotranspiration (ETc), 50% ETc, and 50% ETc with 1000 ppm PS (weekly sprayed on leaves for 11 weeks). Both DI treatments (50% ETc and 50% ETc + PS) reduced plant height by 7.39% and 9.17%, leaf number by 16.99% and 7.03%, and total biomass by 21.13% and 20.58%, respectively, compared to 100% ETc. Notably, under DI, PS-treated plants maintained several parameters equivalent to the 100% ETc treatment, including flower bud emergence, blooming period, green bract number, effective quantum yield of PSII (ΔF/Fm′), and electron transport rate (ETR). In addition, PS application increased leaf area by 8.11% and compactness index by 9.80% relative to untreated plants. Photosynthetic rate, ΔF/Fm′, and ETR increased by 31.52%, 13.63%, and 9.93%, while non-photochemical quenching decreased by 16.51% under water-limited conditions. These findings demonstrate that integrating deficit irrigation with PS foliar application can enhance water use efficiency and maintain ornamental quality in off-season potted Curcuma, promoting sustainable water management in horticulture.