Photosynthetic performance of invasivePinus ponderosaandJuniperus virginianaseedlings under gradual soil water depletion

Abstract

Changes in climate, land management and fire regime have contributed to woody species expansion into grasslands and savannas worldwide. In the USA, Pinus ponderosa P.&C. Lawson and Juniperus virginiana L. are expanding into semiarid grasslands of Nebraska and other regions of the Great Plains. We examined P. ponderosa and J. virginiana seedling response to soil water content, one of the most important limiting factors in semiarid grasslands, to provide insight into their success in the region. Photosynthesis, stomatal conductance, maximum photochemical efficiency of PSII, maximum carboxylation velocity, maximum rate of electron transport, stomatal limitation to photosynthesis, water potential, root‐to‐shoot ratio, and needle nitrogen content were followed under gradual soil water depletion for 40 days. J. virginiana maintained lower Ls, higher A, gs, and initial Fv/Fm, and displayed a more gradual decline in Vcmax and Jmax with increasing water deficit compared to P. ponderosa. J. virginiana also invested more in roots relative to shoots compared to P. ponderosa. Fv/Fm showed high PSII resistance to dehydration in both species. Photoinhibition was observed at ∼30% of field capacity. Soil water content was a better predictor of A and gs than Ψ, indicating that there are other growth factors controlling physiological processes under increased water stress. The two species followed different strategies to succeed in semiarid grasslands. P. ponderosa seedlings behaved like a drought‐avoidant species with strong stomatal control, while J. virginiana was more of a drought‐tolerant species, maintaining physiological activity at lower soil water content. Differences between the studied species and the ecological implications are discussed.

Ecophysiological responses of native invasive woody Juniperus virginiana L. to resource availability and stand characteristics in the semiarid grasslands of the Nebraska Sandhills

“…Understanding the dynamics and peak of these parameters are critical for accurately modeling and forecasting energy budgets and NPP (Hamada et al 2016). J. virginiana is considered a drought tolerant species (Bihmidine et al 2010) and has the ability to maintain stomatal opening and photosynthetic activity at relatively low water potentials (Eggemeyer et al 2006, Willson et al 2008, reaching xylem cavitation and 50% loss of conductivity at Ψ w = -5.8 [MPa] in stems and Ψ w = -4.9 [MPa] in roots (Willson et al 2008), values that were not reached in this study. J. virginiana expands and survives in arid and semiarid environments because it has significant plasticity in water uptake (Eggemeyer et al 2009, Caterina et al 2014) and access to deeper soil layers (roots can reach 7 m deep) where water is available during the periods of low water availability (Walker and Noy-Meir 1982).…”

“…The variable fluorescence (F v ) is the difference between F 0 and F m . When measured on darkadapted needles, F v /F m is proportional to the maximum potential quantum yield of photosynthesis (Bihmidine et al 2010). Predawn (ψ pre ) [MPa] and midday (ψ mid ) [MPa] water potentials were measured using a pressure chamber (PMS Instrument Co., Albany OR, US).…”

“…were determined with an infra-red gas analyzer, with a 6 cm 2 chamber mounted with a LED light source (LICOR 6400 -02B; LICOR Inc., Lincoln NE, US). Measurements were conducted at light saturation -PAR was set at 1,500 μmol(photon) m -2 s -1 (Eggemeyer et al 2006, Bihmidine et al 2010) -and were conducted between 10:00 and 14:00 h solar time in winter, and 09:00 and 14:00 h solar time during the growing season. After completion of each measurement, and due to the scale-like foliage of J. virginiana, foliage material in the chamber was collected and measured with a leaf area meter (LICOR 3000; LICOR Inc., Lincoln NE, US) to correct for gasexchange measurements.…”

“…After completion of each measurement, and due to the scale-like foliage of J. virginiana, foliage material in the chamber was collected and measured with a leaf area meter (LICOR 3000; LICOR Inc., Lincoln NE, US) to correct for gasexchange measurements. The response of photosynthesis to intercellular CO2 concentration (P N /C i curve) was determined at light saturation following the protocol described in Long and Bernacchi (2003), Bihmidine et al (2010), and Bihmidine et al (2014). ] were calculated for each P N /C i curve by nonlinear regression using the curve fitting utility (Sharkey et al 2007).…”

Biohydrologic effects of eastern redcedar encroachment into grassland, Oklahoma, USA

“…The grass model run attempted to mimic grassland that started to transpire in April and ceased to transpire at the end of October. In contrast, the next model run attempted to model two of eastern redcedar's salient features-a continuous propensity to transpire throughout all months of the year and the ability to extract water from the soil even at high suctions due to its strategy of drought tolerance (Bihmidine et al 2010). Precipitation interception was not explicitly modeled for either run in the present study because it is not yet well known for eastern redcedar.…”