Classificações de estratégia das plantas explicam performance ecofisiológica e a montagem das comunidades

Abstract

Identifying plant eco-physiological strategies is key to predict species performance and changes in plant communities under global change-type droughts. Based on plant functional traits, ecological strategies describe how species respond to general stresses and disturbances (e.g. CSR scheme; Competitor - C%, Stress-tolerant - S% or Ruderal - R%), while physiological strategies describe how species respond specifically to drought (e.g. Levitt’s scheme; dehydration Tolerance, Avoidance or Escape). Other classifications describe how different eco-physiological mechanisms interacts to determine plant survival under drought (e.g. Tcrit scheme; time for a plant to reach lethal levels of water stress). Here we assess (i) the relationship between these three schemes and (ii) whether these explain plant growth rate and community assemblage. We hypothesized that (i) plant with lower stress-tolerance (lower S%) exhibit lower dehydration tolerance, takes less time to reach water stress (lower Tcrit), and thus (ii) exhibit lower growth rates during dry season. Methods: We measured 13 morphological and physiological traits in 10 woody species at Campos de altitude (tropical mountain grasslands with seasonal water deficit) and their growth rates during dry and wet seasons. Results: All species exhibit S% strategy but differed in the degree of stress-tolerance (62-96%) and in the main physiological mechanism of drought response (Hydraulic capacitance vs. Embolism resistance), describing a spectrum from more acquisitive water use (S% species that avoid dehydration; S-avoiders) to more conservative water use (S% species that tolerate dehydration; S-tolerants). According to Tcrit, S-avoiders are less vulnerable to drought (higher Tcrit), and there was no relationship between Tcrit and plant growth rate during dry season. S-avoiders exhibit slower growth during dry and wet seasons, but this relationship was not significant with the S% strategy, only with the physiological strategies (i.e. avoider species grew slower). Discussion: The existence of plants with S% strategy but different physiological strategies is possible because CSR scheme describe only the primary ecological function of a species (e.g. stress-tolerance; S%), but not how this function is performed over time (e.g. avoiding or tolerating dehydration). Such as S% strategy, the Tcrit index did not explain species growth during drought (dry season) because both schemes group different physiological strategies into same category, thus it cannot detect the different role of each mechanism for plant performance. The fact that species with more acquisitive water use (S-avoiders) grow slower even during wet season may be associated with greater evaporative demand at Campos de altitude, as atmospheric drought can cause water stress on plants even with soil water availability. Our study highlights the importance of distinguishing plant physiological strategies to predict species performance and detect specific mechanisms of environmental filtering (drought origin: soil vs. atmosphere), showing that plants that avoid dehydration are more vulnerable to atmospheric drought