Chlorophyll fluorescence, predawn water potential and photosynthesis in precipitation pulse‐driven ecosystems – implications for ecological studies

Abstract

Summary 1.A major research focus in population and community ecology is to establish a mechanistic understanding of plant interactions and demographic responses. The first step towards this mechanistic approach relies on understanding the differences in stress caused by different environmental conditions. Leaf-level photosynthetic rate ( A ) within and among plant populations provides important insight into population and community processes, but is difficult to acquire with sufficient replication under field conditions. Instead, chlorophyll fluorescence ( F v / F m ) and predawn water potential ( Ψ pd ) are often used in arid and semi-arid ecosystems. 2. F v / F m reflects the photoactivation status of photosystem II (PSII), whereas Ψ pd indicates water availability in the rhizosphere. Here we compare these indices with A in two perennial C 4 grasses (native Heteropogon contortus and invasive Eragrostis lehmanniana ) and in seedlings of the C 3 shrub Prosopis velutina growing on highly contrasting sandy loam and loamy clay soils in experimental plots. Measurements were made the day prior to and up to 7 days following a 39-mm rainfall pulse after 2 months of drought. 3. A was more sensitive across a broad range of environmental conditions, whereas F v / F m and Ψ pd only responded to periods of protracted drought. The use of these measures was further complicated because their values varied daily and we observed different time-lags in their response to precipitation pulses. 4. We suggest sampling schemes and a priori measurements to capture the value that is representative for the question of interest, and that match the pulsed biological activity in these ecosystems. Finally, we suggest the use of these measures in combination with measurements providing integration over longer time periods, such as δ 13 C, δ 18 O and N concentration in bulk leaf tissue.

Conductancia hidráulica foliar y vulnerabilidad a la cavitación disminuyen con la altitud en Phacelia secunda J.F. Gmel. (Boraginaceae)

“…Sin embargo, la menor Kf también se correlaciona con menores tasas de conductancia estomática y de asimilación de carbono, por lo cual las plantas que ven disminuida su Kf ven reducida directamente sus tasas fotosintéticas (Nardini et al 2008, Hubbard et al 2001, Resco et al 2008, Brodribb & Field 2010. Esto podría llegar a ser una limitante en la respuesta fotosintética de estas plantas al incremento en la temperatura proyectada por el cambio climático.…”

Physiological responses to short-term water and light stress in native and invasive plant species in southern California

“…Fewer studies have examined how native and invasive species respond to shorter-term changes (days) in environmental factors (Durand and Goldstein 2001;Yamashita et al 2000) and many of these studies have focused on grasses (Huxman et al 2004;Ignace et al 2007;Resco et al 2008). In this study, we conducted two experiments to investigate stress and stressrecovery of native and invasive species over a seven day period.…”

Plant ecophysiological responses to drought, nocturnal warming and variable climate in the Pannonian sand forest-steppe: results of a six-year climate manipulation experiment

“…1, 5). Resco et al (2008) also reported low predawn Fv/Fm due to lasting photoinhibition after prolonged (a 2-month) drought, which was accompanied by 75% loss of mean maximum assimilation rate for two perennial C4 grasses in the Sonoran (Manzanera & Martínez-Chacón 2007). However, a marked decline in annual shoot growth was observed for P. alba in a simultaneous study at our experimental site in 2003 compared with previous and subsequent years (Peñuelas et al 2007).…”