Does cross-acclimation between drought and freezing stress persist over ecologically relevant time spans? A test using the grass Poa pratensis

The physiochemical characteristics and glycerolipid profile of Cycas panzhihuaensis in response to individual and combined drought and freezing temperature stress

The frequency and intensity of the occurrence of drought (D) events during winter are increasing in most areas of China. To explore the interactive effects of D and freezing temperature (F) on plants of endangered Cycas panzhihuaensis, some physiochemical characteristics and the lipid profile were determined. Drought and F stress had no or little impact on the traits of leaves, which, however, bleached following a combination of D and F treatment (DF). Drought treatment did not affect the chlorophyll fluorescence parameters and the flavonoid content of C. panzhihuaensis. Besides the increase in flavonoid content, a decrease of photochemical efficiency and an increase of heat dissipation were induced by both F and DF treatment, with the effects being greater in the latter treatment. The malondialdehyde content decreased significantly and the total antioxidant capacity increased significantly in the plants exposed to both D and DF treatments. The D treatment did not impact the amount of phospholipids but led to an accumulation of saccharolipids. Additionally, the amount of both phospholipids and saccharolipids remained unchanged following F treatment but decreased significantly following DF treatment compared with those of the control. The unsaturation level did not change significantly in most lipid classes of membrane glycerolipids following various stresses but increased significantly in phosphatidylserine, monogalactosylmonoacylglycerol, digalactosyldiacylglycerol and sulphoquinovosyldiacylglycerol following D or both D and F treatments. Generally, plants of C. panzhihuaensis showed relatively strong tolerance to individual D stress, while D aggravated the F-induced damage, which was likely caused by the degradation of the membrane glycerolipids.

Drought survival and recovery in grasses: Stress intensity and plant-plant interactions impact plant dehydration tolerance

Plant dehydration tolerance confers drought survival in grasses, but the mortality thresholds according to soil water content (SWC), vapour pressure deficit (VPD) and plant-plant interactions are little explored. We compared the dehydration dynamics of leaf meristems, which are the key surviving organs, plant mortality, and recovery of Mediterranean and temperate populations of two perennial grass species, Dactylis glomerata and Festuca arundinacea, grown in monocultures and mixtures under a low-VPD (1.5 kPa) versus a high-VPD drought (2.2 kPa). The lethal drought index (LD₅₀ ), that is, SWC associated with 50% plant mortality, ranged from 2.87% (ψs = -1.68 MPa) to 2.19% (ψs = -4.47 MPa) and reached the lowest values under the low-VPD drought. Populations of D. glomerata were more dehydration-tolerant (lower LD₅₀ ), survived and recovered better than F. arundinacea populations. Plant-plant interactions modified dehydration tolerance and improved post-drought recovery in mixtures compared with monocultures. Water content as low as 20.7%-36.1% in leaf meristems allowed 50% of plants to survive. We conclude that meristem dehydration causes plant mortality and that drought acclimation can increase dehydration tolerance. Genetic diversity, acclimation and plant-plant interactions are essential sources of dehydration tolerance variability to consider when predicting drought-induced mortality.

Is a seasonally reduced growth potential a convergent strategy to survive drought and frost in plants?

BACKGROUND

Plants have adapted to survive seasonal life-threatening frost and drought. However, the timing and frequency of such events are impacted by climate change, jeopardizing plant survival. Understanding better the strategies of survival to dehydration stress is therefore timely and can be enhanced by the cross-fertilization of research between disciplines (ecology, physiology), models (woody, herbaceous species) and types of stress (drought, frost).

SCOPE

We build upon the 'growth-stress survival' trade-off, which underpins the identification of global plant strategies across environments along a 'fast-slow' economics spectrum. Although phenological adaptations such as dormancy are crucial to survive stress, plant global strategies along the fast-slow economic spectrum rarely integrate growth variations across seasons. We argue that the growth-stress survival trade-off can be a useful framework to identify convergent plant ecophysiological strategies to survive both frost and drought. We review evidence that reduced physiological activity, embolism resistance and dehydration tolerance of meristematic tissues are interdependent strategies that determine thresholds of mortality among plants under severe frost and drought. We show that complete dormancy, i.e. programmed growth cessation, before stress occurrence, minimizes water flows and maximizes dehydration tolerance during seasonal life-threatening stresses. We propose that incomplete dormancy, i.e. the programmed reduction of growth potential during the harshest seasons, could be an overlooked but major adaptation across plants. Quantifying stress survival in a range of non-dormant versus winter- or summer-dormant plants, should reveal to what extent incomplete to complete dormancy could represent a proxy for dehydration tolerance and stress survival.

CONCLUSIONS

Our review of the strategies involved in dehydration stress survival suggests that winter and summer dormancy are insufficiently acknowledged as plant ecological strategies. Incorporating a seasonal fast-slow economics spectrum into global plant strategies improves our understanding of plant resilience to seasonal stress and refines our prevision of plant adaptation to extreme climatic events.

Interactions of plant growth responses to spring freezing and summer drought: a multispecies comparison

PREMISE OF THE STUDY

Freezing and drought both result in cellular dehydration, and similar physiological responses to these stressors may result in cross acclimation, whereby prior freezing exposure increases subsequent drought tolerance. We examined how spring freezing influences summer drought tolerance for a range of herbaceous old field species: 6 graminoids (Agrostis stolonifera, Arrhenatherum elatius, Bromus inermis, Festuca rubra, Lolium perenne, Poa compressa) and 2 forbs (Plantago lanceolata, Securigera varia), with the goal of examining the generality of cross acclimation responses.

METHODS

We exposed the plants to -5°C in the spring and to a 3-week summer drought, and harvested the plants after a 3-week watering/recovery period. We also measured leaf soluble proteins and sugars to explore the potential mechanisms before and during drought stress.

KEY RESULTS

For Agrostis stolonifera, Bromus inermis, Lolium perenne, Plantago lanceolata, and Poa compressa there was evidence of cross acclimation based on aboveground or belowground biomass, with a reduction in the severity of the drought effect for the plants previously exposed to freezing. Freezing and drought effects were additive for Arrhenatherum elatius, and for the remaining two species the test of the freezing-drought interaction was inconclusive, because significant drought and freezing effects did not co-occur. When present, freezing-drought interactions were not correlated with changes in leaf soluble protein or sugars.

CONCLUSIONS

Our results reveal that the phenomenon of freezing-drought cross acclimation appears to be common in herbaceous species, and variation among species in cross acclimation indicates that multiple stresses could alter relative species abundances in plant communities.