Spatial and Seasonal Variations of Standardized Photosynthetic Parameters under Different Environmental Conditions for Young Planted Larix olgensis Henry Trees

Qiang Liu,Fengri Li

doi:10.3390/f9090522

Abstract

Understanding the spatial and seasonal variations in leaf physiology is critical for accurately modeling the carbon uptake, physiological processes and growth of entire canopies and stands. For a 17-year-old Larix olgensis Henry plantation, vertical whorl-by-whorl sampling and analyses of seasonally repeated measurements of major photosynthetic parameters were conducted, and the correlations between photosynthetic parameters and environmental conditions, leaf morphological traits and spatial position within the crown were analyzed. According to the correlations, the photosynthetic parameters were standardized based on the environmental conditions to avoid the influence of the changing environment on the patterns of spatial and seasonal variations of photosynthetic parameters. The results showed that the standardized light-saturated net photosynthetic rate (SPmax), standardized dark respiration (SRd) and standardized stomatal conductance under saturated light (Sgs-sat) were all negatively related to the relative depth into the crown (RDINC) throughout the growing season. However, their vertical patterns were different during the development of the phenological phase. In addition, different gradients of environmental conditions also influenced the values and the range of the vertical variation in photosynthesis. High temperature and low humidity usually resulted in smaller values and weaker vertical variations of SPmax and Sgs-sat, but larger values and more obvious vertical variations in SRd. SPmax and Sgs-sat usually exhibited a parabolic seasonal pattern in different vertical positions within the crown; however, SRd generally followed a concave pattern. These seasonal patterns were all weaker with increasing RDINC. Different environments also exhibited a significant influence on the seasonal patterns of photosynthesis. We suggested that standardization is necessary before analyzing spatial and seasonal variations. A single environmental condition could not represent the spatial and seasonal patterns under all gradients of the environment. Spatial and seasonal variations should be simultaneously analyzed because they are related to each other.

Highlights

Light-saturated net photosynthetic rate (Pmax ), dark respiration (Rd ) and stomatal conductance are representative photosynthetic parameters that generally exhibit significant spatial variations, especially in the vertical direction [1,2,3,4]
It is necessary to eliminate the influence of changing environments before analyzing the spatial and seasonal variations in the photosynthetic parameters
The results showed that c0 and c1 were both strongly correlated with relative depth into the crown (RDINC) and Leaf mass per area (LMA)

Summary

Introduction

Light-saturated net photosynthetic rate (Pmax ), dark respiration (Rd ) and stomatal conductance (gs ) are representative photosynthetic parameters that generally exhibit significant spatial variations, especially in the vertical direction [1,2,3,4]. Pmax and Rd generally decrease with increasing depth into the crown [1,4,10] because the light environment is the core factor determining leaf development [10,11,12,13,14]. This behavior is more obvious in dense stands. The vertical LMA patterns are the result of the adaptation of leaves to both the light environment [11,14,20] and hydraulic constraints [25]. LMA is closely associated with mesophyll conductivity to carbon dioxide [3,26] and usually exhibits strong correlations with photosynthetic indicators [24,27,28]

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Conclusion