Sap flow, leaf-level gas exchange and spectral responses to drought in Pinus sylvestris, Pinus pinea and Pinus halepensis

Abstract

In a climate change scenario, Mediterranean forest species such as pines may be endangered by rising temperatures and reduced precipitation, thus calling for studies on the transpiration and water balance in pines. In this paper, the response of young plants of Pinus sylvestris L., Pinus pinea L. and Pinus halepensis Mill. to different irrigation treatments has been studied. Significant differences were found in water potential, sap flow, leaf-level gas exchange and spectral variables. P. sylvestris had higher pre-dawn and midday water potentials, sap flow rates and leaf-level gas exchange rates compared to the other two species in well-watered conditions. Vapor pressure gradient correlated with stomatal conductance, net assimilation and transpiration, but the association between stomatal conductance and sap flow was weak. The environmental variables more strongly associated with sap flow were solar radiation and reference evapo-transpiration, especially in the well-watered plants, but those associations were weaker in the stressed plants. All three pine species showed the isohydric, drought-avoiding strategy common in the genus Pinus, maintaining relatively high water potentials in dry conditions. Nevertheless, P. halepensis showed a water-saving strategy, with a stomatal closure behavior under drought. Stomatal regulation was less strict in P. sylvestris, closer to a water-spending pattern, while P. pinea showed an intermediate behavior. Significant differences were recorded among species in spectral reflectance in the visible and infra-red regions. Photochemical Reflectance Index, Normalized Difference Vegetation Index and combinations of other ratios permitted the discrimination among the three pine species. These spectral variables showed association with sap flow rate, water potential and leaflevel gas exchange variables. Both cluster analysis and k-means classification discriminated Scots pine and Aleppo pine in two different groups. On the other hand, Stone pine showed differences in spectral behavior depending on the hydric status of the plants. Well-watered Stone pine plants had the same spectral behavior as Scots pine, while the plants subjected to drought stress were closer to Aleppo pine plants in spectral response. These findings may help to quantify the impacts of early and mid-summer water deficit on Mediterranean pines in future climate regimes.

The Photochemical Reflectance Index (PRI) Captures the Ecohydrologic Sensitivity of a Semiarid Mixed Conifer Forest

“…(T air − T leaf ) in crop systems (Rossini et al, 2013;Suarez et al, 2008). Our results agree with Marino et al (2014) who showed a linear relationship between sap flux density and leaf-level PRI in olive trees (R 2 = 0.42), and Manzanera et al (2017) who showed significant correlation between sap flow rate and single-tree PRI (R 2 = 0.62) in juvenile potted pines. We build upon these previous efforts by reporting for the first time, to our knowledge, a relationship between PRI and sap flow in a natural mature forest using novel canopy measurements of seasonal PRI at daily resolution.…”

“…While a number of studies in crop systems have demonstrated the link between seasonal PRI and measures or proxies of plant hydraulics (Magney et al, 2016; Rossini et al, 2013; Sarlikioti et al, 2010; Suarez et al, 2008; Zarco‐Tejada et al, 2012), or shown that PRI is a good indicator of leaf water status (Ripullone et al, 2011; Sun et al, 2014), few have attempted to relate PRI to sap flow rates (Manzanera et al, 2017; Marino et al, 2014); although PRI has been shown to vary with a proxy for transpiration ( T air − T leaf ) in crop systems (Rossini et al, 2013; Suarez et al, 2008). Our results agree with Marino et al (2014) who showed a linear relationship between sap flux density and leaf‐level PRI in olive trees ( R 2 = 0.42), and Manzanera et al (2017) who showed significant correlation between sap flow rate and single‐tree PRI ( R 2 = 0.62) in juvenile potted pines. We build upon these previous efforts by reporting for the first time, to our knowledge, a relationship between PRI and sap flow in a natural mature forest using novel canopy measurements of seasonal PRI at daily resolution.…”

“…However, the influence of precipitation pulses in semi-arid ecosystems can cause functional parameters to decouple over relatively short time scales (Huxman et al, 2004). Sap flow response exhibited a ~2 day lagged response behind PRI during rain events with extremely low vapor pressure deficit While a number of studies in crop systems have demonstrated the link between seasonal PRI and measures or proxies of plant hydraulics (Magney et al, 2016;Rossini et al, 2013;Sarlikioti et al, 2010;Suarez et al, 2008;Zarco-Tejada et al, 2012), or shown that PRI is a good indicator of leaf water status (Ripullone et al, 2011;Sun et al, 2014), few have attempted to relate PRI to sap flow rates (Manzanera et al, 2017;Marino et al, 2014);…”

Mixed Pine Forests in a Hotter and Drier World: The Great Resilience to Drought of Aleppo Pine Benefits It Over Other Coexisting Pine Species

“…Salazar-Tortosa et al, 2018). In this sense, the weaker stomatal control of P. halepensis and P. pinea (Manzanera et al, 2016) can help these species to maintain growth and tolerate dry periods better than P. nigra or P. sylvestris. Another potential explanation for the greater resilience capacity of P. halepensis and P. pinea can be found in their greater capacity to invest more in belowground organs in response to drought (Sarris and Mazza, 2021).…”

Long-term effect of fertilization on stone pine growth and cone production

“…Stone pine is mostly distributed in coastal areas (Vendramin et al 2008), which are considered one of the best sites for growth (Bussotti 1997;Campelo et al 2007;Manzanera et al 2016); in the coasts of Italy and Spain, soils are alluvial, volcanic (Costantini et al 2004), or littoral dunes (Muñoz and Gracía 2009;Piraino et al 2012). However, Handling Editor: Barry A. Gardiner Contribution of the co-authors VL designed the study, directed the projects that funded the study, and wrote most of the paper.…”