Growth potential limits drought morphological plasticity in seedlings from six Eucalyptus provenances

Rainfall fluctuation causes the invasive plant Prosopis juliflora to adapt ecophysiologically and change phenotypically

Understanding the impact of rainfall variability on the ecophysiology of invasive plants in tropical grasslands is crucial for sustainable ecosystem management. Climate change alters rainfall patterns, which, in turn, may influence the functional traits and physiological responses of plants. Recent studies have explored how fluctuating precipitation affects plant growth and broader ecological dynamics. In this study, we examined these effects on Prosopis juliflora under three different rainfall treatments using rainout shelters: low rainfall (LR, 500 mm, 50% less than ambient), normal rainfall (NR, 1000 mm, representing average ambient rainfall), and high rainfall (HR, 1400 mm, 40% more than ambient). Each shelter was divided into three replicate plots (2 m x 2 m) in a randomized block design. P. juliflora seedlings (20 seedlings per subplot) were transplanted into each subplot within a 4m2 area, with a 0.5 m distance between each plant, and data were collected one year after plot establishment (2020). The physiological parameters measured included leaf traits, growth metrics such as biomass, height, diameter, photosynthetic rate, leaf area (LA), specific leaf area (SLA), leaf carbon (LC), the leaf carbon-to-nitrogen (C/N) ratio, and the root-to-shoot ratio. These parameters showed significant positive responses to changes in precipitation i.e. increase with the increase in rainfall. However, water use efficiency (WUE), leaf nitrogen (LN), leaf dry matter content (LDMC), and root length (RL) showed negative responses i.e. decrease with the increase in rainfall and were highest in the LR plots. Our findings suggest that the ecophysiology and functional traits of P. juliflora are strongly influenced by rainfall variability. The species exhibits considerable phenotypic plasticity, thriving in both drought and elevated precipitation conditions. This adaptability has important implications for its invasive potential and the overall functioning of ecosystems under shifting climatic conditions.

Young temperate tree species show different fine root acclimation capacity to growing season water availability

Background and aims

Changes in water availability during the growing season are becoming more frequent due to climate change. Our study aimed to compare the fine-root acclimation capacity (plasticity) of six temperate tree species aged six years and exposed to high or low growing season soil water availability over five years.

Methods

Root samples were collected from the five upper strata of mineral soil to a total soil depth of 30 cm in monoculture plots of Acer saccharum Marsh., Betula papyrifera Marsh., Larix laricina K. Koch, Pinus strobus L., Picea glauca (Moench) Voss and Quercus rubra L. established at the International Diversity Experiment Network with Trees (IDENT) field experiment in Sault Ste. Marie, Ontario, Canada. Four replicates of each monoculture were subjected to high or low water availability treatments.

Results

Absorptive fine root density increased by 67% for Larix laricina, and 90% for Picea glauca, under the high-water availability treatment at 0-5 cm soil depth. The two late successional, slower growing tree species, Acer saccharum and Picea glauca, showed higher plasticity in absorptive fine root biomass in the upper 5 cm of soil (PIv = 0.36 & 0.54 respectively), and lower plasticity in fine root depth over the entire 30 cm soil profile compared to the early successional, faster growing tree species Betula papyrifera and Larix laricina.

Conclusion

Temperate tree species show contrasting acclimation responses in absorptive fine root biomass and rooting depth to differences in water availability. Some of these responses vary with tree species successional status and seem to benefit both early and late successional tree species.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11104-023-06377-w.

Plant Size Plays an Important Role in Plant Responses to Low Water Availability and Defoliation in Two Woody Leguminosae Species

Plant size influences plant responses to combined environmental factors under climate change. However, their roles in plant ecophysiological responses are not fully understood. Two rapidly growing Leguminosae species (Robinia pseudoacacia and Amorpha fruticosa) were used to examine plant responses to combined drought and defoliation treatments (two levels of both treatments). Both 1.5 month-old seedlings and 3 month-old seedlings were grown in a greenhouse, and seedling growth, leaf gas exchanges, stem hydraulics, and concentrations of non-structural carbohydrates were determined after 60 days of treatment. Our results indicated defoliation had no significant effect on plant height, basal diameter, and total biomass whatever plant sizes and species. Under the low water availability treatment, the defoliated seedlings significantly increased by 24% in stem water potential compared with non-defoliated seedlings in large R. pseudoacacia. Compared with the high water availability in large non-defoliated R. pseudoacacia seedlings, the low water availability significantly reduced by 26% in stem starch concentration to maintain the stem soluble sugar concentration stable, but not in small R. pseudoacacia seedlings. We also found a negative correlation between leaf and root soluble sugar concentration under low water availability in A. fruticosa. The results demonstrate defoliation could relieve the effect of low water availability in large seedlings. Large seedlings had more compensatory mechanisms in response to defoliation and drought treatments than small seedlings, thus species with large carbon reserves are more recommended for vegetation restoration under combined drought and defoliation conditions. Future studies with more species are crucial for obtaining more rigorous conclusions.

A Simple Method for Simulating Drought Effects on Plants

Drought is expected to increase in frequency and severity in many regions in the future, so it is important to improve our understanding of how drought affects plant functional traits and ecological interactions. Imposing experimental water deficits is key to gaining this understanding, but has been hindered by logistic difficulties in maintaining consistently low water availability for plants. Here, we describe a simple method for applying soil water deficits to potted plants in glasshouse experiments. We modified an existing method (the "Snow and Tingey system") in order to apply a gradual, moderate water deficit to 50 plant species of different life forms (grasses, vines, shrubs, trees). The method requires less maintenance and manual handling compared to other water deficit methods, so it can be used for extended periods of time and is relatively inexpensive to implement. With only a few modifications, it is possible to easily establish and maintain soil water deficits of differing intensity and duration, as well as to incorporate interacting stress factors. We tested this method by measuring physiological responses to an applied water deficit in a subset of 11 tree/shrub species with a wide range of drought tolerances and water-use strategies. For this subgroup of species, stomatal conductance was 2-17 times lower in droughted plants than controls, although only half of the species (5 out of 11) experienced midday leaf water potentials that exceeded their turgor loss (i.e., wilting) point. Leaf temperatures were up to 8°C higher in droughted plants than controls, indicating that droughted plants are at greater risk of thermal damage, relative to unstressed plants. The largest leaf temperature differences (between droughted and well-watered plants) were in species with high rates of water loss. Rapid osmotic adjustment was observed in leaves of five species when drought stress was combined with an experimental heatwave. These results highlight the potential value of further ecological and physiological experiments utilizing this simple water deficit method to study plant responses to drought stress.