ASSESSMENT OF CARBON DIOXIDE SEQUESTRATION POTENTIAL OF SELECTED TREE SPECIES IN BHARATHIDASAN UNIVERSITY MAIN CAMPUS THROUGH PHYSIOLOGICAL AND BIOCHEMICAL PROFILING MECHANISMS

Abstract

Selecting tree species for institutional and urban afforestation programs across semi-arid South Asia has traditionally relied on historical preferences or aesthetic criteria, without biochemical validation of interspecific carbon fixation capacity. This study establishes a unified structural-metabolic profile by quantifying five core carbon-processing enzymes alongside leaf-level gas exchange parameters and allometric biomass partitioning across ten co-occurring tropical tree species (Acacia nilotica, Pithecellobium dulce, Couroupita guianensis, Butea monosperma, Sapindus emarginatus, Neolamarckia cadamba, Gmelina arborea, Prosopis cineraria, Dalbergia latifolia and Cassia roxburghii) under identical peak-summer microclimatic field conditions at Bharathidasan University campus, Tiruchirappalli, Tamil Nadu, India. The results reveal a clear metabolic hierarchy wherein upstream enzymatic efficiency directly limits downstream stomatal gas transport and long-term structural carbon storage. Prosopis cineraria emerged as the most efficient carbon sink, displaying the highest carbonic anhydrase (CA) activity (8.95 × 10^-8 U mg^-1 protein), the most responsive Rubisco activation (lowest residual absorbance: 0.81 at 340 nm), and elevated photorespiratory protection via glycolate oxidase (1.32 μmol mg^-1 protein min^-1) and catalase (1.42 μmol mg^-1 protein min^-1). This superior kinetic throughput supported a net photosynthetic rate (Pn = 19.2 μmol CO₂ m^-2 s^-1) and a total individual biomass accumulation of ~14,960 kg (~25,804 kg CO₂ eq). A multi-trait Carbon Sequestration Index (CSI) stratified the ten species into three distinct afforestation tiers, providing an empirical, biochemically-validated framework for selecting high-performance tree species for regional climate management initiatives under India's 2030 Nationally Determined Contribution (NDC) targets.