CMG GardenNtes #132 Plant Structures: Rts Outline: Functins, page 2 Structure, page 2 Types f rts, page 3 Depth and spread, page 4 Beneficial micrrganism assciatins, page 5 Thught questins: Explain the science behind the questin. Last summer during a hme remdeling prject we raised the sil level 12 in the yard. This summer my trees lk stressed with small yellwish leaves. I dn t see any insects. Culd the prblems be related t the sil change? My cntractr assured us that trees are deep rted. Since yu can t see the rt system, what are the abve grund symptms f rt and sil related bl? The rts are the beginning f the vascular system pipeline that mves water and minerals frm the sil up t the leaves and fruits. Rts make up arund nefurth t ne-third f the ttal dry weight f a plant. The ttal length f rt tissues in a single rye plant is arund 380 miles! T functin, rts must have adequate levels f sil xygen. Sil cmpactin r waterlgged sil situatins, reducing sil xygen levels, will kill rts and lead t a shallw rt system. The structure and grwth habits f rts have a prnunced effect n Size and vigr f the plants Adaptatin t certain sils Respnse t cultural practices Because they are ut f sight, rts are ften ut f mind. They are widely verlked as t their significance in plant health. The majrity f all plant prblems start with sil/rt prblems. 132-1
Functins Anchr and supprt plants Absrb and cnduct water and minerals Stre prducts f phtsynthesis (carbhydrates, sugars, prteins) Winter survival f perennials Hrticultural uses Fd and feed Prpagatin Sil ersin cntrl Structure Epidermis The uter layer f cells Rt hairs Absrptive unicellular extensins f epidermal cells f a rt. These tiny, hair-like structures functin as the majr site f water and mineral uptake. Rt hairs are very delicate and subject t desiccatin. Rt hairs are easily destryed in transplanting. [Figure 1.] Crtex Primary tissues f a rt brdered n the utside by the epidermis and n the inside by the enddermis. In a carrt, the crtex becmes a strage rgan. Figure 1. Rt hairs are an extensin f the epidermis. Enddermis A single layer f cells in a rt that separates the crtex tissues frm the pericycle. Pericycle A layer f cells immediately inside the enddermis. Branch rts arise frm the pericycle. Vascular system Phlem tissue cnducts prducts f phtsynthesis frm leaves thrughut plant including dwn t the rts. Xylem tissue cnducts water and minerals up frm the rts up thrugh the plant. Zne f maturatin Area where cells frm distinct tissues that becme functining rts. Zne f elngatin Area where new cells are enlarging. Meristematic zne 132-2
Rt tip meristem Regin f cell divisin that supprts rt elngatin, fund at the rt tips just behind the rt cap. Rt cap A thimble-shaped grup f thick-walled cells at the rt tip serves as a hard hat t push thugh sil. The rt cap prtects the tender meristem tissues. Figure 2. Lateral view f rt Types f Rts Fibrus Prfusely branched rts that ccupy a large vlume f shallw sil arund a plant's base (petunias, beans, peas). Taprt Main, dwnward- grwing rt with limited branching, where sils permit (carrts, beets, radishes). Adventitius rts arise at an unexpected place. Fr example, the brace rts n crn and the shrt whitish bumps alng a tmat stem are adventitius rts. Figure 3. Rt types Left: Fibrus rt system f crn Right: Taprt system f carrt Aerial rts arise frm abve-grund stem tissues. On English ivy and pisn ivy, the aerial rts supprt the vine. Aerial rts are cmmn n phildendrns, pths, and Christmas cactus. Lateral rt Side rt Sinker rts make a sharp dive int deeper sils, fllwing sil cracks where xygen is available. Sinker rts are cmmn n sme tree species. Strage r Tuberus rt Enlarged rts that serve as strage rgans (Canada thistle, mrning glry, sweet ptat, dahlia). Depth and Spread The depth and spread f rts are dependent n the inherent grwth characteristics 132-3
f the plant and the sil s texture and structure. Rts require adequate levels f sil xygen, s grwth habit will be a factr f the sil s large pre space where xygen is available. In cmpacted and clayey sils, rts will be shallw, remaining near the surface where xygen is available. In drughty sils, the rt system will spread farther, mining a larger sil area fr misture and minerals. Figure 4. Typical rting pattern f trees, shallw and spreading It is difficult t predict rt spread f any plant. Under favrable grwing cnditins, the typical rt spread f a tree includes: 90-95% in tp 36 inches 50% in tp 12 inches Spreads 2-3 times tree s height r canpy (drip-line) spread In cmpacted clayey sils, the typical rt spread f trees includes: 90-95% in tp 12 inches r less 50% in tp 4 inches Ptentially spreads five plus times the tree s height r canpy (drip-line) spread Sme plants are genetically prgrammed t have very deep, spreading rt systems (i.e., they are mre tlerant f lw sil xygen levels). This grwth habit is an envirnmental adaptatin. Examples include bindweed and prairie grasses. Sil type is a key factr in water penetratin and rt uptake. Where sil allws, the primary water extractin depth extends t: Flwers 18-24 Turf 24 Vegetables 24 Shade trees 24-60 Beneficial Micrrganism Assciatins Mycrrhizae are specific beneficial sil fungi frming symbitic (mutually beneficial) assciatins with rts. While the rle f mycrrhizae is nt fully understd, they functin t expand the rt s cntact with the sil prfile, 132-4
enhancing water and nutrient uptake. Fr additinal infrmatin, refer t the CMG GardenNtes #212, The Living Sil. Rhizbium is a beneficial sil bacterium that frms a symbitic relatinship with plants, primarily thse in the bean/pea family. These bacteria make atmspheric nitrgen available t plants. Rhizbium typically frms ndules n the rts f plants. These may be mistaken fr insect injury r defrmity. When alfalfa, a member f the bean/pea family, is left t mature then tilled int a field, it is cnsidered "green manure" because the plant is rich in nitrgen due t the Rhizbium in the rts. Additinal Infrmatin CMG GardenNtes n Btany: #121 Hrticulture Classificatin Terms #136 Plant Structures: Fruit #122 Taxnmic Classificatin #137 Plant Structures: Seeds #131 Plant Structures: Cells, Tissues, #141 Plant Grwth Factrs: Phtsynthesis, and Structures Respiratin and Transpiratin #132 Plant Structures: Rts #142 Plant Grwth Factrs: Light #133 Plant Structures: Stems #143 Plant Grwth Factrs: Temperature #134 Plant Structures: Leaves #144 Plant Grwth Factrs: Water #135 Plant Structures: Flwers #145 Plant Grwth Factrs: Hrmnes Authrs: David Whiting, Cnsumer Hrticulture Specialist (retired), Clrad State University Extensin; with Michael Rll and Larry Vickerman (frmer CSU Extensin emplyees). Line drawings by Sctt Jhnsn and David Whiting. Revised by Patti O Neal, Rberta Tlan, Mary Small, CSU Extensin. Clrad Master Gardener GardenNtes are available nline at www.cmg.clstate.edu. Clrad Master Gardener training is made pssible, in part, by a grant frm the Clrad Garden Shw, Inc. Clrad State University, U.S. Department f Agriculture and Clrad cunties cperating. Extensin prgrams are available t all withut discriminatin. N endrsement f prducts mentined is intended nr is criticism implied f prducts nt mentined. Cpyright 2003-2018. Clrad State University Extensin. All Rights Reserved. CMG GardenNtes may be reprduced, withut change r additins, fr nnprfit educatinal use. Revised July 2016 132-5